Go fighter/thief multiclass. Pure class thieves get only 1 attack per round, hit worse and can't wear helmets to protect from critical hits. Half-orc is best for doing damage.

I had a brain error and somehow forgot what the OP asked about halfway through reading the answers people were giving him. I also really should have phrased it better. I would say my recommendation is actually for each and every character be a 2 class multi-class. :)

When I said straight classes are better I was thinking casters and fighter types, who benefit more from specializing early on (higher spell levels, or better fighter stats). I just didn't think about thieves who are to me Imoen, sitting in the back plinking with arrows while the combatants actually kill things... the 6th party member assigned for scouting, traps, locks, pickpocket, etc rather than being a real combatant. Silly considering this is titled "theif/fighter question".

So, that being said let me do a reevaluation specifically for a thief/fighter v thief...
Well, thieves do need to those extra skill points with the level cap being so low in BG1

BG1 XP cap is 89,000, while in the Tales of the Sword Coast expansion, the limit is raised to 161,000
@89000XP your max level is 8 for a straight thief (thac0 17). For multiclass its fighter 5/thief 6 (thac0 16)
@161000XP your max level is 10 for a straight theif (thac0 16) and 7 fighter/8 thief for multiclass (thac0 14, +0.5 melee attacks per round)
Multiclass fighter/thief can also specialize in a weapon for -1 thac0, +2 damage, +0.5 melee attacks/round.
I am assuming your thief is using a shortbow for safety though (let the tanks tank :P), so those attacks per round bonuses disappear.

In both you are sacrificing 50 points of your much needed and fairly scarce skill points for a small but meaningful damage advantage which you don't really need (thanks to the rest of the party being properly min/maxed). Also an HP boost. Also, this doesn't take into account you potentially using stealth in combat.

Eventually though your thief gets all the skill points s/he needs at which point you want to dual class out of it. But this is not going to happen in BG1. People love dual classing imoen in BG2 into mage.

Actually, in BG2 she already *has* been dual classed to Mage, she begins BG2 as a Th->Mu.

This was done partly because it was extremely common for players in BG1 to dual class her to Mage - it makes great sense since she is too weak to really backstab, she can get all the skill points she needs in F/RT and OL fairly quickly and can still get to respectable Mage levels in TotSC.

While dualling her wasn't universal, it was common enough that the game designers took note of the fact [one reason she is not a pure class Thief in BG2 - the other being that if the PC chose a non-magic using class, then you couldn't find a MU until you had gotten out of the initial dungeon...] Thus, as a Th->MU Dual class, Immy filled two important class slots for a new party, without the PC being forced to play either, to make up for their lack in the initial dungeon.

I remember back on the old Bioware boards, the discussion was not so much whether to dual Imoen, but rather, when to do it. :) Much discussion over which specialist school she should take too - Conjurer and Illusionist seemed to be the favorites. [Of course, importing from BG1 to BG2 strips you of your school, if you have dualled to Mage, so they did the same to her and present her as an unspecialized Mage in BG2.]

Staff is the way to go and the Ulgoth's Beard inn has a nice one (+3)… race is up to you.

Very interesting. I know questions like these are asked often. Unfortunately most of my experience is with BG2. I've only played the original a time or two. I want to change that and I want to enjoy and experience the game on its own merits as opposed to being just a gateway to BG2. So this character I more than likely won't take into BG2. I just want to play the original by itself. With the lower level cap I just wasn't sure which direction to go with my thief character. I plan on only using a bow and backstabbing. I won't be wading into general melee. So my original worry was that my fighter/thief would level too slowly.

One more thing if you are going to play BG1/, I recommend using console + mods to give yourself a bottomless bag of holding.
Until I have done it I always quit halfway through BG1 because it got too tedious, but with this I don't have to backtrack 3 times per area map (I am too OCD to just abandon loot I know is worth little).

Say... when you said BG1/TotSC only, did you mean on their own engine or on via EasyTuTu?

Well originally I was trying to play it on the original engine using some of the minor modifications listed in the sticky. But it didn't work out too well so I'm using Easy TuTu. I got everything installed and ready to go. Just trying to figure out the whole fighter/thief vs pure thief. But I appreciate the tip on the bag of holding. Good idea.

Actually, since thieves hit level 7 at 40,000 xp, fighter/thieves will hit fighter 6/thief 7 in vanilla BG. That's kind of moot, though, since GoG's version includes TotSC.

Halflings get bonuses to slings, I believe. Anyways, multiclass thieves get enough points to max out Find Traps and Open Locks just fine, and those are the only skills you actually need thieves for.

It seems halflings get the bonus with slings and darts. So which is better one to use for a single class thief or fighter/thief? Slings only have 1 APR but are easier to use and there are more magical ones. Darts get 3 APR but have less range and magic ones are expensive. What do you guys think?

Slings all the way, especially for a Fighter/Thief. Both slings and bullets get added Strength bonus, making them hit harder even than most bows. They are all about damage per hit, not hits per round.

Really? I did not know that. I never really played a halfling much and never really used slings all that seriously. Very good to know Hickory. At first I figured darts would be better. Again very informative.