The spin bike will force you to find a spot to keep it out. Which will make it very convenient.

The trainer will lure you into putting it away when you're finished. You'll have to set it up each time.

That said, I have a trainer. Even if I wanted the spin bike I've got nowhere to put it. I can't say that my trainer doesn't have enough resistance. If I have the bike in a 53x11 I can't spin 60 rpms for much time at all, if I can even get it there.

The trainers are definitely noisy. My fluid is very loud. Probably quieter than others, but it's still loud.