In that case, you're just like the rest of us, there are lots of threads on this topic and much has been said before, if you give exacting requirements, people can really help you out, but otherwise, hire at your next game, and ask as many people as possible if you might be able to hold their gun and then aim each down the sights. Shoot it if allowed, some people assume you will, but I always ask. I even swapped with someone who was hiring once for a few shots in the middle of an engagement.
I don't recommend shopping here, tax is guaranteed, shipping does not include [mandatory] handling fees, but this page is great for finding ideas:
http://www.evike.com/shop/21/672/
M4's are recommended because they're the most common (and commonly desired), and common equals cheaper, more competitive manufactures, and cheaper up/side-grades.
Once you have UKARA you can import guns - though it can be worth paying more to get it from inside europe. Be sure to check the weight of guns when buying them, two guns of the exact type can have 2+ KGs of weight difference.
Guns are generally priced 20-80, 80-130, 130-180, 180-250, £250+ in my observations, two guns from similar price brackets are going to be similar quality in many cases - as are two from the same manufacturer/range in adjacent brackets. These brackets do not include batteries, chargers, slings, or bags: cheaper guns do often come with NiMh batteries and chargers included.
80-130 is a great starting point, gets you off hiring, you have not spent too much if you run into problems - even if those problems are in part caused by not spending much, you have a cheaper throwaway gun for lending to friends after you buy your 'main' gun, you can learn about AEGs from a cheaper gun - most guns allegedly get worse when you open the insides for the first time. You have a backup when your main gun has issues.
You also won't mind so much that first time you fall on it.
Don't forget face protection when you stop hiring. Buy a sling.