Dsimpson and Haeveron regard FMs and FMTs as the game's strongest characters and I think they're right in that assessment. This is often counterintuitive to people who haven't tried those mixes because you can't get time stop (or in the case of FM get it late) and can't wear armor, but mage buffs have such great synergies with fighters that the deficiencies are more than offset by the advantages.
Other very strong characters are cleric/rangers (though less so now that they get fewer druid spells), half-orc fighter/thieves or fighter/clerics, inquisitors, and as others have mentioned sorcerers and bards. You won't go wrong picking any of them.
There are also a couple of joinable NPCs that are worth mentioning because of the special features they have. Jaheira, for example, can not only wear heavy armor (which only FDs can do) but is also able to cast some cleric-only spells like raise dead and zone of sweet air, making her the most versatile druid character in the game. And Edwin gets, essentially, the spells per day of a sorcerer while being able to access the much broader spellbook of a mage, making him the best arcane caster in the game (if you can put up with what some regard as his grating personality).
the Bhaal essences scattered across his progeny must be rejoined through the deaths of each Bhaalspawn, whose divine essences then return to the source seen at the end of BG1.
The in-game lore is silent on whether it is possible to resurrect Bhaalspawn after
their divine essences have rejoined the pool, though the complete crumbling of the Bhaalspawns' mortal shells after death would rule out the game's resurrection spells which require bodies or at least body parts to function properly.
This is why Sarevok needed CHARNAME to
do the resurrection some other way, and even then, it wasn't possible to bring Sarevok back with his divine essence intact as it had already entered the pool.
Imoen is different, because
the devs changed her into a Bhaalspawn for BG2 after previously envisioning her as a normal human in BG1. Because the devs viewed her as a normal human in BG1, she could be resurrected like any other normal human without her body crumbling to dust. The devs were thus faced with a difficult conundrum, because the intended shock of discovering Imoen's Bhaalspawn status in BG2 would have been nullified if they retroactively patched BG1 to make her non-resurrectable (because you would see her body crumbling to dust in BG1 and realize the two of you share a common heritage, which you then inexplicably wouldn't be able to explore or even ask her about until BG2).
This does represent a plot hole, yes, but the cause is out-of-game human error rather than inconsistent in-game lore.
There are a couple of downsides to shamans that haven't been mentioned yet. The biggest of these is, they can't multiclass with fighter and hence are going to be much less melee-viable than a fighter/druid (or ranger/cleric) would be. They also can't do other things while summoning spirits, which in practice means players tend to get bored and ignore spirit-summoning (though in fairness the spirits actually aren't bad). Finally, shamans can't get a stronghold of any type, which doesn't matter much if you're sticking to BG1/SoD but hurts in BG2.
The big advantage of shamans, though, is that you can give them situationally useful spells like slow poison and negative plane protection without much weakening their combat-casting prowess. This in turn frees up your other divine casters to memorize fewer defensive/utility spells and more offensive or DPS-enhancing spells (in the same way that sorcerers can learn identify and protection from petrification so your other mages can focus on magic missile and chromatic orb). Having both a shaman and a fighter/druid (or ranger/cleric) can work well.
One other point worth mentioning is that, while shamans are stereotyped as casting only druid spells, they actually get a couple of pretty good shaman-only spells.
Yes, they changed sleep back to the way it originally worked. If you hit someone with a weapon, they remain sleeping for the duration of a spell (to the great benefit of BG1's many ankheg farmers).
The main question to ask with a BG1 sorcerer is whether you're going to take the character into SoD/BG2 and, if so, whether it will grate on you to be carrying spells that become useless toward the end of BG1 and remain dead weight throughout SoD/BG2. If you're doing a BG1-only run, it is a no-brainer to take sleep as your go-to spell along with shield/armor and perhaps blindness as well. If on the other hand your goal is to have a completely optimized BG2 character, it would be better to stick with spells like chromatic orb and magic missile that remain useful throughout your adventuring career.
Due to the large number of foes who can only be hurt by blunt weapons, and the small number of decent clubs in the game, I wouldn't recommend going with a druid even though there are some decent druid spells in the game. I'd recommend F/C and R/C for your second and third slots.
Due to the small number of mage scrolls in the game, and the small number of spells per level that are useful in IWD, sorcerers are a great choice. You want at least one and possibly two of these in the party.
Two key things to know about HoF mode are 1) your summoned monsters get the same boost enemies receive and 2) enemy hit point pools are so large that immobilization becomes more important than DPS.
Overall, I'd do something like this with your party:
Elven F/M/T who generally uses longswords and casts melee buffs like mirror image and stoneskin
Half-orc F/C with 19 strength who uses flails
Half-elf R/C who uses maces, war hammers, and eventually flails
Additional melee character with the flavor you want: cavalier, F/M/C, or archer (but keep in mind that blunt weapons are king in this game so arrows will be ineffective against a fair number of enemies)
Sorcerer who mainly casts stun/immobilize spells (chromatic orb, emotion hopelessness) and summons (animate dead when he can, monster summoning VII later)