I own both Sacred and BD. Have to say I like BD a lot better. Sacred has its good points, but I don't like how Ascaron makes you uninstall Nero Burning Rom and Alcohol 120% just so you can play. That kind of takeover shouldn't be allowed. And I found that after installing all the updates and such, the buggy copy protection drivers ground my system to a stand still when I wasn't even playing (moving large files took forever because it would send for a bit, freeze, send a bit, freeze). I had to reformat my computer just get rid of it. Since I got rid of it I've had no problems. But besides that, the graphics are pretty good, but the multiplayer aspect should weed out the rest of the bugs, and I do like how it shows you what percentage of the map you've discovered. Adding Tristram from Diablo is pretty cool addition too.
Beyond Divinity is my favourite though. I prefer the random item system better in it than Sacred. I found a lot of useless garbage in Sacred, and I find a lot of good stuff in Beyond Divinity. That's what I like. The battlefields are awesome, too. I was very interested when I heard about it before BD's release. I just wish the monsters would respawn and match your level so that you don't have to clear out a bunch of levels that give you nothing experience wise (to prevent abuse, they could set a level cap on each of the dungeons. That'd work well).
Either way, they're both good, and I can't wait for DivDiv2.