Zidane, Steiner, Amarant, and Garnet. Strength for the first 3 and then Garnet's healing and summoning abilities.

Sometimes I'll switch up Amarant with Freya though to mix it up a bit.

Zidane (trance moves do like 9999)

Garnet (White Mage Support

Vivi ( Flare)

Steiner ( I forgot the move name but when he has very low HP you can initiate and attack that does the difference between his Max and Current HP. And since his hp is relatively high that was useful)

Zidane (trance moves do like 9999)
Thievery can do 9999 damage as well - it takes quite a lot of stealing, but if you steal frequently throughout the game then you should be pretty close by disc 4. Once Thievery is doing 9999 damage, you won't want to trance unless you want to nuke multiple enemies at once - something that can be left to other party members. Soul Blade, Sacrifice and Thievery can be much more useful than Zidane's Dyne abilities.

Normally I use Zidane, Vivi, Eiko and Amarant as my final party.

A few for party building: three physical characters seems to be better than three magical characters. Because she's effectively a combined Vivi and Eiko, Garnet works best on 3P/1M parties or 2P/2M parties in which the other magical character is Quina. In 2P/2M parties, Freya or Amarant are much better choices for the second physical character than Steiner (and in Memoria you can ditch Zidane and take both, if you like). Even when making a 3P/1M party I'd think twice before including Steiner.

In his defence, Steiner can go solo more effectively than the other characters (although a Steiner SCC isn't exactly the most exciting FFIX challenge), and if you want to use an all-physical party then Charge! can be quite a handy attack.

Zidane: Obligatory. His attacks are alright once you get him some decent weapons.

Steiner: Raw strength. His abilities are somewhat useful, but have a low accuracy rate. However, his swords have high power, so he's an indefinite choice on any play through.

Vivi: Exactly the same as Steiner, only for magic. For most of the game, his spells deal an ass-load of damage. Flare raws mah sawks.

Garnet: Probably not as tactically useful as Eiko, but she's good none the less. Her Eidolons seem more appealing to me because of the element choice, so I always stick with her. R1 + Curaga = <3

My Final Party Was
Zidane
Freya
Quina
Armarant

Mainly Because They Had Interesting Ability's

Zidane: Steal away from those bosses!
Eiko: You do need someone to heal and who doesnt have to wait until someone actually needs to be healed cuz her attacks are too weak( Garnet ).
Freya: White draw is just so friggin OP and Dragon Breath is a good attack.
Amarant: Altho I like him more in combination with vivi (curse!), without him he's strong enough: throw + no mercy ! ^^

:up: same as