Curb has the better theme music, that's for sure
I think the big difference is that Larry and Brent both experience unpleasant situations and difficult people in their lives, but with Larry he's almost always in the right or the wronged party, where as Brent usually isn't and makes his own problems most of the time
It's the same with Curb Vs Alan Partridge
I think we're generally supposed to root for Larry, as most of the people he deals with are normally much more disagreeable than he is, but with Brent and Partridge, I think we're supposed to enjoy watching them get their comeuppance
I could be wrong though