Limes can't live without healers and I'm sure of that... because when they transform, they can die easily. And they're usually str/dmg based (on items), so their HP is very low.
I must say healers is a must in any stage/raid. This would make everything more safe + secure, and will save money from buying pots.
Anyways I'll exclude limes:
Best 2: 1 healer + 1 sieg. If the sieg is good at offence, then a FS with buffs would be good. If the sieg isn't, then maybe a battle healer may be necessary. Ex: casting attack buff to make things easier.
Best 3: 1 healer, 1 sieg and a dainn. Same things apply to the above, and a dainn may be handy because their ice walls are very useful.
Best 4: 1 healer, 1 dainn, [1 or 2 siegs] OR [1 sieg and 1 thief]
everything applies to the above but thieves are usually only useful due to their skill "Turn back time" which is a skill that reset the cooldown times of the skills. However, it's probably unecessary unless there are limes or lv 60 skills. So I'd rather get a sieg than a thief, but it's your own preferences. Thieves may be useful if they're good at backstabbing or something :3