Hi -
As far as the "Best Kind', well (like a lot of things in this life) it usually seems to be just a tad more than we can afford.
To answer your question seriously, I'd think it depends a lot on what exactly you want (or need) for the tire-monitor to do. I'd love to have gotten the kind that transmits temperature as well as pressure, and the kind that mounts inside the tire (vs on the valve-stem), and so on. I even found one kind that has a rotating-fitting to each wheel-hub and is connected to the on-board air-pump, so you can fill the tires individually WHILE MOVING!. However, those models are a bit (ok, waaaaaay) out of my price-range. So I got the Pressure-Pro kind, and yes they do mount externally and do not have a temperature monitor, and I have to run real fast to fill a tire if I'm traveling.
But they do what I needed them to do, and they do it quite well (reference my teething problems in other posts). For the money I spent, I'm quite happy in the value for the money as well as the safety and security. RV-Upgrade.com has 'em.
The final thing that firmly convinced me to get some kind of tire-monitor was when I talked to a guy that said he got a flat on his toad and that big 400hp Cummins ISL kept right on pulling the toad til it melted the tire right down to the wheel-rim. Said he didn't even know it until someone flagged him down.
HTH