Some semi-rambling thoughts about the classes, which hopefully will encourage others to contribute their opinions...Fighting classes:
Fighter: Whew, they can dish out the damage. The stamina regen is very nice early on, but doesn't seem to be as useful later. One good feature: you can focus on only 4 stats (Str, Vit, Dex, Spd) unless you plan to switch. I switched my fighter to a lord at 9th level, and I think that was a mistake in some ways, altho the lord's HP regen is better IMO than the fighter's stamina regen.
Class switching notes: The best switches I can think of, would be to samurai or ninja. NOT for the magic, but for crits.
Lord, Valk: Might be tough going initially, but if you start the game with one of these, you probably can live without a dedicated priest in the party. Magic Screen and Armorplate are long-duration spells, but you cast them so much anyway that you improve your skills in those areas fairly quickly.
Samurai: My Felpurr has been the weakest of my fighters, but that's beginning to change. One problem with samurai is that they really want to improve *6* different stats (everything but Piety), and this is just hard to do. But, as the Int and Senses have been creeping up, I'm starting to see more crits out of my samurai. Magically, they're slower...more combat spells, but they're coming late and are useful in some circumstances, but more often, you need to use a more effective attack mode. That means less practice, and therefore slower development.
Monk, Ninja: The only example I have here is RFS-81, and a little time spent with my first party (only reached 9th level, was getting extremely frustrated and decided to restart). I *like* monks. Martial arts skill develops fast...lots of attacks. Nice to have someone on Psionic spellbook too, which is somewhat hard to get otherwise. Ninjas share many of the same benefits, and toss in thieving...but may tend to be skill point hogs, as thieving is a skill where you don't get that much practice.
Ranger: Auto-searching, and the search skill, are godsends initially, especially for me without my old Wiz7 parties to import. Great rearguard character, obviously, standing back with the bow. Since ranged combat is the class strength, interestingly, you can do well to NOT push Speed...let him sit back while the fighters wail away on the front-line opposition, then pick off the next rank.
Class switching: I don't see any benefit from switching out of any of these. Your magical skills start late and develop slowly; you'll still be gaining useful abilities for most of the game.
To be continued...