The below has nothing to do with character concept. Character concept is completely different from efficiency. I do not claim that character concept should take a back seat to efficiency.
However, it is important for people to understand the mechanics so that they don't end up with a "useless" character (In their opinion.)
Do not, I repeat, do not tell me I am a twink/munchkin/rollplayer etc. (I already know.)
This assumes you are not taking any PrCs.
Good Multiclassers:
Fighter
Barbarian
Rogue
One level of Ranger
When multiclassing, always take one of the above classes and either:
1) Combine with another "good" multiclasser.
2) Combine with one of the other classes.
Do not take any of the following classes and combine them, unless you are prepared to have less power than a single class character. i.e:
No Sorcerer/Cleric/Wizard
Bad Multiclassers:
Cleric
Monk
Bard
Paladin
Multiple Levels of Ranger
Worst Multiclassers:
Wizard
Sorcerer
Druid
In order of the most effective characters:
1) Single Class
or
1) Best + Best
3) Best + Bad
4) Best + Worst
5) Bad + Bad
6) Bad + Worst
7) Worst + Worst
I have only ever seen one effective three or four class character:
(Fighter + Barbarian + One level of Ranger + Rogue)
When PrCs are added into the mix, and the PrC requires a multiclass decision, make sure that what you are giving up by multiclassing is balanced by the effectiveness of the PrC.
For example:
The True Necromancer gains the ability to Create Undead at CL 14. A Single Classed Cleric, on the other hand, gains the same ability at CL 11. In effect, with this PrC, you are giving up the highest level of Cleric Spells for the lowest level of Wizard spells. IMHO, this is just not worth it.
Now on to reality:
Each roleplaying group is different. Meaning: Not all of the above is the same from group to group. In some groups, Diplomacy is the best skill and Weapon Specialization is a wasted feat.
In your group, if everyone multiclasses, and the DM drops the difficulty of encounters or tailors the encounter specifically to the PCs, then the multiclass issue will be less of a burden.
However, in my experience, players like their characters to have one thing that they are really good at that sets them apart from the other PCs; be it disarming traps, bluffing the guards or slaying the beasts.
And just like in the real world, specialists are better at doing specialized tasks, and generalists don't excel at any one thing.
