Oh I dunno...The good ones to me are Ark, Odin, Bahamut, Madeen and Phoenix...I used Odin alot during the early game but switched to Bahamut later on because it looked cooler. Bahamut's not that "expensive" to summon if you got the half MP ability. Plus, I took away the magic stones from the Odin's sword ability so I could use them for other purposes like Auto-Haste. Also, its easy to deal 9999 damage to enemies, like when I fought the Nova Dragon and used Bahamut (HAHA I'll show you WHOS the boss dragon around here)