Better in what way, Dorkenstein? Your char in BG1 gets a boost to each stat from special books. Combine it with another +1 boost from Watcher's Keep and you get a total +2 to all stats. If you start a new char in BG2, obviously this bonus will be lost (so only a total of +1). If you play the first part with TuTu, you can go whichever class you like. What do you think is a "cool" profession? Answer that and play the game. You will beat it regardless of your choice.
For soloing there are better and worse classes. You can hardly expect to solo the game as a mage or a cleric. What you need it a heavy hitter with lots of HP - like a Kensai/Mage dual (didn't try this one myself), a Shapeshifter (with Weimer's Fix - a lot of fun!

) or a FMT (Fighter/Mage/Thief multi-class) - the last one becomes a one man army as he will be able to use all items (Thief HLA), drop deadly traps (also Thief HLA), get Whirlwind/Critical Blow attacks (Fighter HLA), get a temp boost to physical dmg resistance (this one's crazy

- Fighter HLA) and cast deadly lvl10 spells (Dragon Breath - Mage HLA - deadly). With proper items you can make a lot of spells almost instant cast (add Finger of Death, Abi-Zail-something-more-here spells, Death Spell, etc

) which means you will dish out crazy amounts of damage in a round.
So, to sum up, just think which class do you think sounds cool and just play
EDIT: As for Irenicus' Dungeon... did you install Tactics?

Cause I remember those pesky duergar from the Tactics mod as in a regular game there wereo nly goblins (one-shot'ers) and only a few groups of duergars.