It is common sense to use a Air/Fuel ratio gauge to measure A/F, but some ppl say to use a exhaust temp gauge. Which should be the way to go?

 

The problem with just adding a a/f ratio gauge is it uses your stock O2 which is not as accurate as an EGT gauge. If it was a a/f gauge using a wide band O2 it would work very well. But most wide band O2 a/f meters run between $2500-$10,000. So the EGT is the cheapest way to go with better accuracy, than your typicall add on a/f gauge.
87 TII
94 Formula

 

Or you could go to this site http://www.techedge.com.au/vehicle/wbo2/default.htm and make your own wide band 02 sensor at a bit lower price. And skip the AIR/FUEL gauge and use a small digital meter. Just a couple of different ways to look at this.