3DR if they are in stock. They are optimized for the APM and new users. Will be a little easier to set up with the built in Mission Planner utility. Personally I prefer modules in the 900mhz range. Check out this link from sparkfun on the matter.
What is the data rate of the xbee compared to the 3DR? I have a new 3DR with default options and it seams a little slower than my old xbee?
The 3DR radio (SiLabs Si1000 chip radio) has better receive sensitivity, faster data rate, more transmit power, and is cheaper. Xbees are very weak and buggy, just check the thousands of "problem with my xbee" posts here.
The 3DR radio beats the Xbee on every conceivable spec, so there's no question which is better. The Xbee does have FCC certification though, so if you're working on mass producing a commercial product it might be cheaper to use the Xbees.
433mhz is not a good option at the moment, I'd go with the 915.
Could you expand on your reasoning of the 433MHz modules not being a good choice at the moment?
DC, the better authority on this is Andrew Tridgell. Read this forum post Andrew put up in April. Either radios, when available, should work well for you. Hope this helps.
433MHz is very close to the frequency of most noise on the USB bus. You also need a much larger antenna and there are more RF design issues and antenna issues with the lower frequency.
The 3DR radio wasn't really designed with much attention to RF issues and 915 is much more forgiving in that respect IME.
The PA (amplifier) matching uses low pass filters, so if you get the 915 you should be able to do some testing at 433 if you'd like, but obviously the reverse is not true.
Generally, lower frequencies will go further. But in this case I'd suggest that the 915 is the better choice until they get the kinks worked out better.
You're also not going to like the 433mhz regulations if you live in the US. If you can even figure them out, you're going to have to do a lot of work to be legal on this band. If you're concerned about being legal you will certainly want to avoid the 433 version as there's no firmware yet that will make the radio put out a legal signal.
What about the legality issues if the user have a General Class HAM License? I know the radios can be configured to stay within frequency limits offered to the HAM, however, I am not sure of the power restrictions.
There is a thread here about the issue. Seems to be a lot of disagreement and confusion on what the law actually is, which sections apply, and what it all means.
Here is some discussion, but few conclusions...
There's all sorts of foolishness in the law. In the end I think everyone gives up and just does what they want.
In any case there's more restrictions and hassle in the 433 band, which makes it much more likely that you'll be out of compliance.
Sure glad I didn’t get a 433. Since it’s close to other frequencies I’m not sure if it will ever be as solid as 915. The main problem is that some countries restrict the use of 915.
As an American, where radio was invented, I give you permission to use 915mhz.
Americans did not invent radio.
Radio's evolution is long and very international indeed.
But yes, americans were the first to patent it.