The perennial question. Ask 10 Airsofters this question and you will get 11 answers and none of them will be wrong. I will start of by saying that there has never been a better choice of well priced Airsoft guns of all shapes and styles at every price point.
First as to the style of gun, get whatever you like the look of. In Airsoft there is much less performance difference between a submachine gun, a carbine or a full battle rifle than in real life. The only real constraint is weight and length, a gun that is too big and heavy can be unwieldy in some environments. AR15 style rifles are popular for good reason as they are so modular and can be built into almost anything and parts are readily available, only downside is everyone has one. Other platforms range in terms of options and parts support from generally very good (Marui clone AK’s, MP5s etc.) to very bad (any VFC GBBR).
There are generally three routes to entry:
(1) buy a cheep gun with a view that you are going to replace it pretty quickly. These are usually polymer bodied AR15 clones. I won’t recommend this approach as the mid priced guns are now so affordable that this is a false economy.
(2) Buy a mid priced gun and then upgrade bits as you go. This is the approach most people take and for good reason. Something like a Specna Edge series rifle can be had for as little as £169.00 (although there are loads to choose from). These will usually be metal bodied AR style rifles (with a smattering of AKs and MP5s). From a mechanical perspective they be Marui clones and will perform well out of the box and unless you choose something really ‘out there’ will have good after market parts support. These will be very serviceable guns on day one and with a wealth of upgrades can be tweaked and upgraded to your hearts content.
(3) Buy your ‘forever gun’ on day one. In this bracket I’ll put any of the high end AEGs (Marui NGRS is the obvious candidate) and any GBBR. The aim here is to save money in the long run by buying the gun you really want at the start and skipping all the intermediate steps. This only really works if you have a very clear idea of what you want on day one and can resist ‘upgrade feaver’ and only change stuff when it breaks. There are a few problems with this approach. (1) The initial outlay is high, (2) Your ideal gun may well evolve as your experience increases (3) gun tinkering is as much a part of the hobby as skirmishing (4) no one really has a forever gun and most people end up with a couple. However if you are sure you are committed to the hobby and have a very clear idea what you want this can make sense.
For what it’s worth when I came back to the hobby after a very long gap I went with option 3, got a Marui NGRS and was very happy, until I decided I needed the realism of a GBBR, so bought a Marui MWS.