I know you're probably hooked on the idea of full suspension now, and I have to say good FS bikes have a lot to offer. However, I'm guessing that you've never ridden a decent hard tail MTB for any length of time. Like I said before, most hard core dirt jumpers/DS racers ride small framed rigid bikes because they are stronger and more reliable (also for DS you can sprint faster). If you learn to jump well and develop good technique on a rigid bike you'll be a much better airman when you get on an FS rig and are fully able to exploit its capabilities. Once again I would recommend you to get this kind of bike, you don't want to be shelling out money all the time for bent pivot bolts (if indeed you can replace them) worn bushings, bent rear triangles etc etc etc (the list of possible woes with FS bikes is almost endless- ask any DH racer how much they spend per year on replacing broken bits, you'll be amazed). You, your wallet, and your riding will all be much better off in the long run if you buy a simple, strong bike that you can maintain yourself.
If I can't convince you of this (and it seems like I can't), I will try and offer some advice below on the bikes you are considering.
Between the Mongeese, I'd have to see a price difference to say whether it's worth it. Certainly the fork upgrade is worth having, the rims ought to last a little better, and the shifters are a bit better, but I wouldn't have thought it should add up to more than $200-$250 more. If it's less than that it's probably worth it. This is an indication of the trouble with how manufacturers spec bikes these days. They're happy to 'upgrade' those bits people notice, forks, rear derailleur etc; but when it comes to the things that make a difference to the long term function of the bike (hubs, BB, bearings instead of bushings in FS etc) forget about it! You'll be lucky to even find BB type even listed on many companies' spec sheets.
As for the Apollo you posted the specs for, I would point out firstly that this is a URT, and it's not an especially long travel fork. This is a bike that is designed more with general riding in mind than the kind of jumping/DH stuff you intend to do.
One final point of advice, is that bike build quality is just as important as specifications on bikes in this price range, if not more so. Now I'm not talking about weld or tube quality (that is fairly consistent), I'm talking about how well assembled it is by your LBS. Now it's possible to just pull that Mongoose or Raceline out of the box, slap a few bits on and it's ready to go in 5 minutes. That same bike will also have you back in the shop every few days to get this or that tightened, or something replaced that broke because it wasn't properly installed. Unfortunately most bike shop owners don't seem to realise this, and go for the "slap it together" approach. I'll list some questions below that you should ask the person who assembled your bike.
- Did you true and tension the wheels?
- Did you check the axle lock nuts?
- Did you tighten the bottom bracket cups?
- Did you press the headset?
Of course, there are lots of other things that should be done in the assembly of a bike, but unless your shop can give an immediate and resounding yes to all these, I'd advise you to go elsewhere. If you feel uncomfortable asking such things (as might be understandable as you're only 13). Check some things for youself. You shouldn't be able to move (front or drive-side)spokes much at all just by squeezing them. Try to move wheels side to side, is there any play? Try pushing on brake pads, do they move? (if your bike has discs try it on another bike, this will be a good indication of how much care the shop takes). Try and twist brake levers on the bar, try and shift the stem on the steerer by holding the wheel in your legs and turning the bars etc etc.
Give the bike you might buy a good going over, if it fails many of these above tests go elsewhere. Also, ask what sort of after sales service the shop offers. If it's only minimal or none, this is a good sign the shop is not confident of it's work. At my old shop customers could come back in as often as they wanted for 1 year after purchase, this is because we were confident in the job we did assembling the bike and were pretty sure nothing would go wrong unless defective or just worn out.
Anyway, I've rambled long enough, I hope you find the bike you're after, and that you're happy with it. Even if you don't take my advice on bike selection, please do take it on shop selection, you'll thank me. The shop that offers you the same bike for $200 less, may not offer the better deal of they've skimped on build quality and after sales service.
Sam.