Actually, I have a lot of music (~80GB worth) and I found rythmbox very crashy. I have found banshee to be a lot more stable.
But I'm not really fussed either way; they're both good (although I hope the crashes in rythmbox get fixed for those who still use it).
I know this is flamebait, but I think the complaints about mono are some of the most fatuous arguments I've seen in recent times. At first when I realised banshee was a .NET/mono app I thought "OMG!". But I later realised that disliking it because the language/runtime is based originally on an MS product is silly. Either the app is good or it isn't.