I've not used the hotels in a business context, but live in BOH, so seeing as you've had no other suggestions...
The Hilton and the Marriott are pretty accomplished, both right in the centre of town, with the Marriott having the larger conference facilities. It's also the better of the two IMHO, and is on the clifftop (the Hilton looks over the town to the sea).
My uncle uses the conference facilities at the Menzies Carlton (
www.bookmenzies.com) which is on the clifftop but a little out of town. As far as I know he's happy with it, but the
www.tripadvisor.com reviews are mixed.
If you're prepared to go a little further, you might want to look into the Haven Hotel in Poole (
www.havenhotel.co.uk) or the Chewton Glen in the New Forest (in a different league -
www.chewtonglen.co.uk). I'd give the Royal Bath a miss - prime location but very tired.