Lots of hotels are close to lots of things. Compare it to London - in terms of size, it depends where and what you want to see.
I always say to 'newbies' it's best to stay near the river, with river views, as it's cooler, more relaxed, and can offer great views. After your first visit (and you will be back!), most people head to Sukhumvit Road (for shopping), or further afield (I like the Lumpini Park location). You can get around Bangkok really easily, so no great shakes where you end up.
It might be best to work backwards from your budget, and then people can make good recommendations?