Let me be the first to respond.
Some people will tell you to forget the trainer and get rollers, and some people will tell you to get a trainer.
I have a Kurt Kinetic Road Machine (fluid trainer) - based on the limited amount of research I did, this came out on top. It has a little speed to power conversion meter you can buy as well to get Watts as your output.
There are many others available, some more expensive and some less so. Depends on what you want to spend.
Note that cycling indoors is quite dull, and I find it hard to overcome the mental agony it seems to cause me. It's also very hot, so you'll probably need a rubber mat to go under your bike, and some big fans.