In my experience which is exclusively sub-£200 budget gnus as that's my budget - I'd say that any of the big names will serve any beginner perfectly well, and most are available under £150.
-CYMA - A good safe bet, they just work and seem to last really well. The CM513 is brilliant, mock suppressor and tons of RIS space. Their AKs are legendary and highly recommended. CM048 is next on my want list. Probably the best choice here.
-JG - Another safe bet, again they just work. Provides "different" platforms like MP5s, M14s, G3s, G36s etc.
-Specna - Their Core series is decent, Edge IMO should be avoided, everyone knows someone who's had an Edge that's had the complicated electronics or notorious Orion gearbox poo itself at an awkward moment and ruining a skirmish day. Would pick a CYMA or LT instead but that's just me.
-Double Eagle - The Honey Badger series has gained a real cult following for lots of features often seen on Gnus double their price - I haven't tried one but lots of fans out there, seeing them appear regularly and everyone has nothing but praise.
-Lancer Tactical - Controversial opinion, but I'd recommend them for beginners, lots of features for the money and imternals seem decent. The plastic they use for construction feels more sturdy than most other manufacturers at this price point. I have the M933 Gen 2. It's great cheap thrills, a real hoot, best 100 quid I spent in airsoft!
-G&G - Have a good rep, excellent quality but their prices seem to have inflated considerably over the past couple of years. Overpriced for what they are IMHO but otherwise a safe bet for something that will just work.
Couple of points to make for beginner AEGs:-
-Don't get too hung up on metal bodies - yes its "more realistic" but a) it makes it heavier and b) the metal used in many airsoft guns, especially at this price point, tends to be pretty shit. Plus plastic doesn't rust...
-Forget "upgrades". Most AEGs are decent out of the box and only require routine maintenance to keep them working nicely. Parts only really need replacing if they get worn out/broken, like hop rubbers, barrels, motors etc. Focus on getting your game good, your aim, your fitness and your tactics and being part of a team. Those are the important things. Fancy high-end pieces or "uPgRaDeD" frankensteins, i.e. the airsoft equivalent of a tarted-up Vauxhall Nova (and just as unreliable, unless done by someone who knows what they are up to), do not make you a better player.
-Snipers, DMRs etc. seem "cool" (and they are to an extent), however its a different way of playing and requires a lot of patience, practice and investment to get right - something that most beginners don't have. Learn the basics first. Learn about communication, team tactics, getting fit, learn your site and the different attack points, defensive points, ways to move, bits you can camp in etc. Once you learn the game you can then look at the different roles within a team and look at things like being a marksman etc.
The most important point in all of this however is something that many miss - HAVE FUN!
Eezer G