I really like the ScanGauge II. I have also worked with Linear Logic to program custom settings for the xGauge. In some cases I wanted to read a different PID (data from the PCM) or I wanted to change the decimal place of data provided.
I feel it has a touch lag, I do wish it was faster, but for the price, you cannot beat it!

I have seen people that basically use an Arduino and ELM327 chip and build their own ScanGauge like device (which would give you better control over the update speed).

Here's a couple interesting threads I created here for the ScanGauge:
https://montecarloforum.com/forum/fw...u-cable-51593/
https://montecarloforum.com/forum/fw...i-cable-51596/
https://montecarloforum.com/forum/fw...ettings-52465/

For the DIYer that wants to play with an Arduino and build their own, here is one of many examples. This one is from a former MCF.com member (zzapultimate).
http://www.justindepewdesign.com/sin...uino-Car-Gauge