I have to agree with thegreenronin, your army is pretty slow, and war machines will help make up for this. I personal like Spear Chukkas, mainly because I know I'd fail at range guessing, but the others look nice as well. I have to disagree with Green Knight, black orcs are great but a bit expensive, and I'd leave it to personal opinion. If you are staying at 2000pts for now I'd say trolls are a little unpredictable, without a ld9 general they aren't as good. For giants personal opinion again. You can't even field special characters under 2000pt (Lords) and I don't like the idea of using them, also its perfectly possible to look good without one, and possible to have a better looking model from the general box, with extra bits and possibly conversion. Considering this is 1500pt you are aiming you can only have 3 characters, so you will have to not use one of them you listed.