Do we have a preferred VIN search at this point?

I understand the limitations...

What's our current favorite?

I still prefer Carfax.  It's far better at finding service records than Autocheck or the others.  

CarFax is still my preferred one, in the past it's caught accidents that Autocheck missed. Depending on how much you're spending on the vehicle, it may not hurt to run both.

I've been amazed at what just googling the 17 digit number can reveal.  I have found past salvage auction photos this way, as well as getting all the way to the previous owners name and number.  

Its not Carfax type info but it can be interesting.  

Also, if it is a Toyota/Scion/Lexus you can get full dealer service records for free by registering at the "owners" section of their website.  With Scion dead, just enter into the Toyota site.