What group-size do you like best?

[Pellinore]

If the characters are balanced I like a 6 person party plus a DM. 4-5 is great, too. I like a well rounded party...

[jopperm2]

I've been playing more D&D 3.5 lately and I'm thinking that if you have a very traditional party of Fighter, Rogue, Cleric, and Wizard, with no weird builds and no multiclass, things will go very well.

With anything more strange though it becomes easier to have an extra person. For instance, if you have a Ranger instead of a fighter, your Rogue and Wizard may take more damage in large battles.

It also depends a lot on what types of adventures you go on. If you face a lot of undead, then you will do well with a Paladin instead of a fighter. If not, that choice is not nearly as useful.

An Illusionist can do very little until high level against mindless enemies such as vermin and undead. etc.

[GawainBS]

A Paladin's increased effectifness against undead is neglible: if they can be turned by him, they're not powerful enough to harm the party significantly. I'd rather use those turn attempts to fuel Divine feats. Those, coupled with the spells, make a Paladin a lot more useful overall than a Fighter.
A Fighter can also be easily replaced by a Druid. It would mean a significant boost in the party's overall power. Up to 6th lvl, the Animal Companion can fill the role of the Fighter, with the Druid providing extra spells. From lvl 6 onward, the Druid can start Wildshaping and still be able to cast spells. A way better "tank" than the Fighter ever will be. There's still the Animal Companion tagging along too.
A decently multiclassed Fighter/Mage can fill that role too, and do some more things. (Like Ftr2/Wiz6/EldritchKnight10/ArchMage2.) Increased size en thus reach, spells and increased mobility.
With some use of low lvl summon spells, or one of the non-core books to use find traps as an alternate trap feature, or another base class, a rogue's detect traps can be easily replaced.
The only two members I'd hate to miss, are the Cleric and the Wizard, and I don't consider Cleric-healing necessary.