There are so many threads just like this one already. Try using the search function at the top of the page as well as reading the faqs, it will save you alot of abuse.
When I started I did extensive research and settled on the Tactical Carbine version of the Classic Army M15A4 as my first gun. In my opinion it's the best of all the possible Armalite versions. You have the shortened M4 carbine barrel, which makes you less likely to smack your barrel off something when turning quickly, combined with the full stock which houses a large battery. Small batteries don't have near the run time of a large battery, not to mention that the reinforced slip ring (the ring that keeps the fore-grip on) is really stong. While this is mostly a good thing and a big step up over CA's previous M15 versions, it makes changing small batteries in the field very difficult if not impossible.
Classic Army's M15A4 series in general is a big step up over their previous versions and as far as stock armalites go they're probably the best. All metal where the real steel version is, the plastic parts where the real steal version is plastic are made of good quality. CA has a deal with Armalite so you get all the proper markings. Plus that deal also goes to show the quality of the manufacture, Armalite wouldn't put their name on a shoddy product.
Internally the gearbox is reinforced metal and all the gears are metal as well. It fires hotter stock then TM's as well, firing at 300-320 fps where your average TM only fires 280-300 fps.
All in all this is a great starter gun if you can afford it. Because it's all metal you don't have to worry nearly as much about breaking it and you won't get any of the wobble that is infamous in stock TM M4/M16's. Unfortunately affording it is the biggest problem, they're not cheap.
To give you an idea of cost (once you get age verified) I got my CA M15A4 from the classifieds, upgraded with a bunch of Systema internals to fire 390fps, for $600 shipped which was a great deal.