I used to run an LC-1 (Bosch sensor). It was a good little sensor. With the programmable outputs you could plug it into your stock ECU, and have it mimic a narrowband (you can re-program the output to have your car idle at a different A/F ratio on the stock computer if you like). It warmed up really quickly too. Good price, but doesn't come with a gauge. If you have a laptop, you can use that as a logging tool.
I currently run an HKS A/F knock amp (NTK sensor). It's super quick to react, very precise,and comes with a gauge (and also has engine knock monitoring built into it). You can input your own reference voltage to it, and have the output offset to match.