There are two ways to select Pokemon – the first is based on the quality of the Pokemon itself, in a standalone environment.  Generally, you will want to consider the following:

-Hit Points – The more the better.

-Capacity to deal damage – It’s important that you have the ability to deal large amounts of damage as would befit a mid or late game situation.

-Capacity to deal Special Conditions – Paralysis, Poison, Confusion, Sleep, and Burn are all useful both for their own effects, as well as the ability to shut down Pokemon Powers.

-Retreat Cost – The cheaper the better – free being preferable.

-Weakness/Resistance – these, along with retreat, are commonly known as bottom stats.

-Energy type as a damage modifier - If your area has lots of Scyther and Gligar, a fighting type Pokemon might not be a good choice because you will frequently see negative damage modifiers based on the Fighting Energy Type (like Fighting Resistance).  Alternatively, if your area sees lots of Wigglytuff and Clefable, which are fighting Weak Pokemon, then fighting Pokemon might be a good choice since they could frequently take advantage of the positive damage modifier of Weakness.

-Speed – Does this card need 4 energy to attack?  Can it get by on 1?  Does it have an attack like Plasma or Energy Absorption which allows for the attachment of additional Energy Cards?  Speed wins games – slow decks simply don’t survive long enough.  It’s highly important to keep your opponent on the defensive as much as possible, because if he or she is concerned with not dying, they can’t be concerning themselves with attack nearly as effectively.  Speed creates offense and pressure, and pressure creates a necessary resource split between offensive and defensive actions for your opponent.  Which is bad for them and good for you.

-Single Energy Attacks – Probably one of the most important qualities to search for in a card – if it can’t attack for a single energy, or worse yet, for two or three, the card is probably bait for Energy Removal and a stolid, painful beating.  Note that “Single Energy” refers to a single energy CARD – an attack like Gligar’s Slash is considered a Single Energy Attack because it can be paid for with a single Double Colorless Energy Card.  A Single Energy Attack uses either a single Basic Energy or two Colorless Energy – Miracle Energy is not considered in the identification of Single Energy Attacks because its “one per deck” rule makes it inconsistent while its “discard after your turn” line makes it illogical to use since it deprives you of the build of an energy base.

-Pre-Evolutions – If a particular Pre-Evolution is outrightly terrible, one must consider this in selecting the line for use in a deck.  Alternatively, if a Pre-Evolution just happens to kick a great deal of tuckus or cover for a weakness of the final intended Evolution, this can often be a massive boon.  An example of this is Golbat and Crobat.  Although Crobat can be rendered quite ineffective by the Grass-Resistant Steelix, the ability of Golbat and Zubat to Poison the defending Pokemon covers for this strategic problem quite well.

-Extra Capabilities – This covers Pokemon Powers and additional effects of attacks.  Cards like Slowking, Murkrow, Chansey, Brock’s Mankey, and countless others, a0re quite popular based on the textual abilities included in their attacks or Powers.
 

The second important factor to consider when selecting Pokemon for your deck is synergy – how well the Pokemon you select work with other cards in your deck.  Most archetypical decks use a synergetic strategy to dominate lesser decks and create a sum that is figuratively more than its parts.  

Synergy of Stall – Perhaps the weakest and least relevant of the strategic synergies that can be examined is the Synergy of Stall.  Basically, if you’re using a slower Pokemon it can often be good to have something like Scyther, Chansey, or a similar low-retreat high-HP Basic Pokemon to simply take a turn or two’s worth of hits while you charge up your attacker on the bench.  Is stalling recommended?  Probably not.  Realistically, a competent player will do all they can to disrupt the stall through use of board control or energy control cards like Gust of Wind, Double Gust, or an Energy Removal type card.  Still, it is a valid strategy – just usually a rather weak one.

Synergy of Energy – Probably the most common form of synergy initially strived for in a deck: to conserve energy required in the deck, you run Pokemon with the same required energy type.  For instance, Rocket’s Zapdos and Electabuzz are often seen together in Unlimited because the cards both run primarily off of Lightning Energy.  This also applies to Special Energy cards – for instance, Scyther and Chansey both make good use of Double Colorless Energy, and thus they are both often seen together.  Through exercising synergetic energy strategy one can afford to run fewer and fewer Energy cards, which means more trainers, and a stronger control of the game.

Synergy of Weakness – If you’re using a Pokemon with a Weakness to a certain type of Pokemon, it can often be wise to run Pokemon with Resistance to that Type.  The example of Chansey and Scyther once again applies in this case.  However, weakness does not always simply refer to the Type of Pokemon that a Pokemon is weak to – sometimes certain Pokemon are weaker to other cards, be they Pokemon or Trainers, and these problems can be mitigated through the playing of other Pokemon that do not share these same problems.  Sneasel is a highly playable card but it is dependant upon a statically limited base of four Darkness and four Rainbow Energy – it has a weakness to cards like Energy Removal and Super Energy Removal.  However, the use of Trainer denial like Slowking or Dark Vileplume can cover for Sneasel’s weakness quite well.

Synergy of Extra Abilities – Sometimes the Pokemon Powers or extra effects of attacks can work together in surprising, and deadly, ways.  For instance, Murkrow and Slowking interact very well due to their Extra Abilities.  Murkrow’s Mean Look attack can eliminate the option of Retreating a Pokemon via the paying of an actual Retreat Cost, whereas Slowking removes the option of retreat through the use of Trainers.  These two Extra Abilities, although they are quite useful on their own, become wickedly effective when combined.  This type of Synergy, combined with the Synergy of Utilities, is generally the basis of the strongest decks in today’s environment.

Synergy of Utilities – This is quite similar to the Synergy of Energy, but instead of revolving around energy type requirements that Pokemon have in common, it deals with beneficial Trainer and Special Energy cards that have additional effects which are especially useful with certain Pokemon.  For instance, Metal Energy’s ability to reduce damage is ridiculously useful with cards like Chansey and Rocket’s Zapdos that damage themselves when they attack.  As another example, high HP Pokemon work well together with Gold Berry, while low HP Pokemon function better with Focus Band.  Beyond that, a higher level synergy could be formed by primarily using Pokemon that work well with one of the aforementioned tools or the other – this way the needs of the Pokemon would only facilitate the inclusion of one of these cards – instead of running two Gold Berry and Two Focus Band, you could easily get away with one or the other, or even three of one of the two options.  This saves card slots in the deck and allows for a) faster access to the cards that you require, when you require them and b) a wider variety of card functions in your deck.

Whew.  So there we go - a guide to selecting your Pokemon, and critiquing your existing ones.  Using the qualities outlined above one should now be able to evaluate individual Pokemon in a complete and thorough manner, and select the right Pokemon for the right job.  But remember - just because something works well in theory doesn't mean it will be successful in the play field.  Practice and playtesting are always important components of victory, and without them, even the best strategy can turn in on itself and perish.

Thanks for reading!
-Gloom