T2 - Fun, fast, gets the blood flowing for super jackpot, but nothing much esle to it.
Stargate - System 3 reliability, wizard modes, best system 3 in almost every ones opinion
Whirlwind - Not super familiar with this title. Alpha numeric (opposed to the other 2 being dot matrix), fun shots, not sure of full rule set.
I would say Stargate if you want the total package for a good price, T2 if you want a easily sellable solid pin with a fun theme, and whirlwind last but mostly because im not familiar with it as much as the other 2.