I've experienced both. Sometimes the conference rate is higher & the hotel weekend or daily rate lower. Sometimes the conference rate is lower & the hotel rate higher. In high rent districts (NYC, Orlando in the summer, etc), the hotel rate is usually higher than the negotiated convention rate. I do what others do - book the convention rate, but check back periodically to see if I can get a better rate & if I can, then I cancel the convention rate.

Also, if it's a large conference the rates are usually negotiated years in advance so if the market was more hotel-friendly (ie, high rates) when contract was signed & then by time of the conference the market was buyer-friendly, quite often you'll see a difference in the rates. But the hotel isn't going to let the conference out of the contract.

I've also seen people get stung because they wait to the last minute to book the lower conference rate because they know the conference is being held there, but don't realize there's a deadline to book by & after that deadline the extra negotiated rooms get dumped back into general inventory and the rates can be much higher.

My rule of thumb is it's always easier to cancel a room than get one at the last minute, so I tend to book conference rooms way in advance & then just monitor the situation.

Cheers.