Heh, looks like we've got all of them except Blastoise Ex here, and I understand why that one doesn't really fit in. I like this idea, actually, as you get a better idea of how the individual cards measure up to the available substitutes. ^^
Base Set Blastoise
I do believe that we are looking at one of the retro cards that would utterly disbalance the modern TCG environment. xD The poképower...is just awesome really, one extra water energy attachment for every pokémon you have in play, and with so many water pokémon having some version of Water Gun to exploit that. The attack reaches a solid 60 damage too, which - in the retro environment - will knock anything out in two turns and with the poképower the rather steep cost of five water energies that this takes becomes quite manageable, especially since it can manage a steady 40 with three (Which is the same as the base set Wartortle's Bite). 100 HP is very good by the old standards (and still formidable today) and this card certainly excels both as active and on the bench, despite the electric weak and troublesome 3 energy retreat. This is one monster of a card and any further empowerment would disbalance it completely. A must-have for any Water based retro deck. 10/10
Dark Blastoise
70 HP leaves this card kind of vulnerable to assault (As Dark pokémon often are) but Hydrocannon can deal a whopping 70 damage in one go with four energies, which seems like a very good deal to me. Rocket tackle seems a bit too risky for me, especially with the low HP this card has, and the lack of a poképower prevents it from supporting other cards. The fact that it has one less retreat cost than the base set edition doesn't really do it much good, though, and the HP is a bit too low. 7.5/10, it's strong in its own right, but not the same kind of vital necessity as the base set one. Works for more aggressively minded water decks, I guess.
Third Blastoise
Energy Cannon is basically a slightly empowered version of the base set Blastoise's Hydro Pump and the fact that any energy goes opens up the possibility for a special energy card or two, but the poképower is kind of counter-productive (Except maybe if you've had all your energy discarded, in which case it's free energy discards), it can also be good if you've got lots of energy in your hand but little to use it on. HP is a solid 100 here, although the art isn't living up to that of the early cards. .___. Oh well, 8/10 since it's a nice, solid attacker.
The bottom one
Both last and least, I see. -.- Bubble is an okayish attack, but with a 2nd stage I'd expect to see something with a bit more umph. Double Cannon is a bit too much of a gamble, as it only exceeds the other Blastoise's Energy Cannon in the 1/4 chance situation that you get heads on both coin tosses, ties with minimum-power Energy Cannon half the time, and does nothing whatsoever on every fourth. There's no poképower either. Basically, this one isn't much good unless you're a devil of a coin tosser and pales in comparison to the Energy Cannon one. The HP is good, but no more so than on the other Blastoise. 3/10, there are really far better alternatives out there. .___.