What it comes down to is this: You need a positive-shift PPM receiver, or a JR PCM receiver. You have many, many choices among positive-shift PPM receivers (including JR's own offerings) and much less choice among JR PCM receivers (there aren't as many models/prices).

The first thing to really understand is that people often confuse their terminology. The companies themselves contribute to this. The biggest bit of confusion is what FM means. It's frequency modulation. FM receivers can be PPM or PCM, generally. PPM is analog encoding. PCM is digital encoding. Both are transmitted via FM. Manufacturers rarely us the term "PPM", instead calling it "FM". That's because most modelers aren't clear--for most people, the choice is between "FM" and PCM. Let's hope I haven't confused this issue for anyone.

PCM, being digital, involves checksums. What's a checksum? It's a way of validating the data the receiver decodes, just like your computer does when you download something from the Internet. Bad data happens, and with PCM it throws away the bad data (packets of data are called frames). If no data or enough bad data is received, that's when a PCM receiver goes into "failsafe". Failsafe isn't all servos returning to neutral, as was stated by another poster. It's the servos going to a pre-set condition. People argue about what that should be, most only agreeing that the throttle should be cut. You'd be surprised how many people never program their failsafe positions, and many people have a misconception that failsafe will somehow save their model. Failsafe is primarily to make a crashing model safer (the engine being cut) rather than save the model from crashing.

PPM just takes it all in. Bad data, no data, the receiver doesn't do anything about it. If your signal is lost or someone turns their transmitter on with the same frequency as yours, there's no "failsafe" position for the servos--they kind of do whatever they want to do. That might sound bad, but in reality either way the model is likely be done in one way or another if there's no good signal.

Far more people use PPM than PCM. PPM is cheaper, you have lots of choices in terms of the receiver you use, and for regular sport flying there are few true advantages to PCM. It really comes down to you making an educated purchase about what your needs are and what your budget is. If you want to stick to PPM, buy from a reputable brand name such as Hitec, JR, Airtronics, or FMA Direct. Saving $10 on a no-name knock off may not be the wisest of choices.