The best one is General Mobile DSTL1 (AKA SciPhone N21). It's the best one, since it is the only one.
I don't know of any other dual-sim Android phone.
I own the DSTL1. The battery life is about 3 days of standby. The dual-sim option works flawlessly.
Unfortunately the screen resolution is quite low and some applications won't run on it. There is no GPS and no 3D acceleration. H.264 videos (for example YouTube) don't play, but it should be fixed with a new ROM release. Also originally the phone doesn't come with Android Market, but there is an unofficial hack which allows you to use Market and install applications from it.
It's not a great phone, but not a bad one.