Our BRU didn't have great selection, was organized in a way that made it hard to find the things they did have, felt kind of dirty, and had just ok customer service (in starting a registry - we didn't buy, return, exchange, etc.).
After going to BBB, there's no comparison - we deleted our BRU registry almost immediately. Customer service was amazing! They had almost everything (including cloth diapers!), it was clean and well organized, prices were at least as good on things I compared, esp. if you use 20% off coupons - and you can use Bed, Bath, & Beyond coupons there as well. As far as the actual store goes, BuyBuy Baby felt very similar to Bed, Bath, & Beyond - they even have the same kind of wall of gadgets and small items in the feeding section as the kitchen gadget wall! I believe the registry completion is the same at both places.
The major drawback could be that there aren't as many locations, so if you want to register there, make sure there's a store close enough to most of your shower guests (not a problem for us, but could be for some). The website also isn't great, but I don't love BRU's website, either. For online shopping, I'm keeping a second registry at Amazon.
Caveat: FTM here and haven't had a shower yet, so I haven't dealt with any returns, etc. But Bed, Bath, & Beyond made all those things super easy with our wedding registry, and since it's the same parent company, I'm assuming it would be pretty much the same.