You'd think they'd keep 2 cards from different sets separate, but w/e...
Regigigas LA 37 is the staple Regigigas card for his deck. 100 HP is excellent for a Basic Pokemon, a x2 Weakness to :fighting: isn't too great with Machamp running around (not to mention he's a Basic to start with, making him already weak to Take Out), no Resistance, and a very expensive :colorless:colorless:colorless:colorless to Retreat. Recover Mechanism is a neat Poke-Body to have, letting you heal any Special Conditions off Regigigas when you attach an Energy. Gigaton Punch is a solid attack, dealing 60 for :colorless:colorless:colorless, plus another 20 and 20 to an opponent's benched Pokemon if you flip Heads. This is your primary Regigigas because it offers the cheapest, most damaging attack of all the basic Regigigas without a drawback (Slow Start for the other LA one, and having to play more Regis for the SF one).
Modified - 9.5/10 (Regigigas is a very solid deck, made possible by this Regigigas and the Lv X form)
Limited - 9/10 (A big Basic that can deal out solid damage with Gigaton Punch)
Unlimited - 1/10 (Not much use here, is bait for GoW and eaten by ER and SER)
Regigigas SF is one of the possible alternatives to your primary Regigigas LA 37. Like its other Regigigas brothers, it has 100 HP, a x2 Weakness to :fighting:, no Resistance, and costing :colorless:colorless:colorless:colorless to Retreat. Regi Form isn't as useful of a Poke-Body, letting you reduce your attack costs by :colorless if Regirock, Regice, and Registeel are in play (which no Regigigas deck should have, besides possibly Regice). Mega Punch is ok at :colorless:colorless for 30 damage, but Giga Power is a bit much at :water::fighting::metal::colorless for 60, plus another 40 if you do 40 to Regigigas. Granted, you're going to need to have all 3 types of Energy attached eventually, but it severely limits you attacking options early on, whereas Regigigas LA 37 can attack with any Energy for roughly the same damage output, without harming himself.
Modified - 7/10 (Not as good as Regigigas LA 37, but still worth considering over 1 if you want)
Limited - 3/10 (Way too many energy types needed to attack, and the other Regis aren't even in the set)
Unlimited - 1/10 (You'll never attack with this thing here)