best AFR gauge setup

I'm sure there are plenty of good ones out there, just stay away from the cheaper ones.
I have an AEM guage in my car and it was a pretty close match to the dyno AFR readout.
As mentioned you will be looking around 12.5:1 at WOT for gasoline but different fuels will require a different AFR for best power. My hemi six made a couple more HP at 12:1 than 12.5:1 but it was small enough that it could have been inconsistencies between runs.