So, finally I get my account unlocked. Coupla things worth discussing:
White and Red Mages have different spells. This is actually tabletop-accurate but means you should probably have one of each. White Mages get Minor Globe of Invulnerability, Confusion, Hold Monster, and Globe of Invulnerability, among others; Red Mages get Mirror Image, Haste, Fire Touch, and Mind Blank, among others. (There's no clear buff/debuff theme to the split, and it has to do with schools of magic in D&D.) TRADEOFF: Red Mage gets fireball at 4th level, which is an advantage if you don't multiclass as you can start throwing fireballs considerably earlier in the game, but if you do the Mirror Image spell is self-only and useful in combat.
Two clerics is adequate for Champions and Queen but may make Death Knights a little tougher because of all the undead (you may have to actually deal with all the level-draining wights running around and may get drained). God choice bears some thought; there are seven, and they each have subtle differences, but the big difference is neutral vs good. The best are Mishakal, which gives healing bonuses (thanks Erebus), Kiri-Jolith which gives you a +1 THAC0, and Majere which turns undead as a cleric two levels higher. TRADEOFF: All these are gods of good; gods of good don't get seventh level spells in Death Knights (can't restore levels lost without a temple)-and remember those wights? So if you're doing a three-party game you may want to invest in a neutral cleric. Sirrion gets burning hands, Shinare gets charm person. Charm Person's a little more useful I think. Reorx will give you a +1 THAC0 if you're a dwarf, so if you make a dwarf fighter/cleric that's a bit of a bonus. (They're limited to 10th level as clerics though.)
I used to be a big ranger/cleric advocate, but enough people pointed out to me that slows down your advancement I'm going to say fighter/cleric is fine...as long as you're a Qualinesti (see below). Ranger is mostly helpful for extra damage against giants (not a big part of the game until the end of Dark Queen of Krynn, when you've got lots of other resources) and one particular druid spell (Protection from Fire) that you can do without. In the Forgotten Realms games, human rangers who get to 9th level and then change class to mages can cast spells in armor, but you can't change classes in Krynn games. Elves can also reach 40th as rangers, which they can't as fighters. But 14th gets you most of your hitpoints and full two attacks.
Qualinesti is better than Silvanesti, especially for fighter/mages. Qualinesti gets to 14th level rather than 10th as fighters (nod to Cael), letting them get a full 2 attacks per round. The Silvanesti can become a 12th level paladin, but who cares? (Qualinesti can also be thieves.)
You can't make a Paladin in Champions, only in Death Knights and Dark Queen. TRADEOFF: They're semi-useful in Death Knights because they can turn undead as a cleric two levels lower (unlike knights), but the knights have better clerical spell ability.
Kender--this is controversial. A lot of people really didn't like the kender in the Dragonlance books; others did. But--for gaming purposes they can be cleric/thieves, though only to 12th level, but have max WIS 16, which prevents use of 6th and 7th level cleric spells. (They will actually get them in Death Knights and lose them in Dark Queen when the programmers figure out the bug.) A small note is that 12th level with the 2-level bump from Majere gets you maximum undead turning ability, so if you want to have a kender Majere may be your best shot. On the other hand using that for a neutral god slot will let you use higher-level spells on your kender in Death Knights. The fear immunity didn't seem to work on Death Knights, but the taunt remains tactically useful through Dark Queen.
(Character creation is full of all these weird traps, where a flavor choice in game 1 screws you over in game 3. This is all covered in the manual for Death Knights and Dark Queen, which of course you didn't read yet. Remember these games were marketed to Dragonlance nerds in the early 90s, who couldn't search the Internet on account of it hadn't been invented but had the manuals memorized and would be happy to write the game company letters (on dead trees!) if they gave an enemy too many hitpoints.)