I am fairly new to airsofting myself as well. I choose to go with a KWA KM4A1 as my first high end purchase for a totally all stock gun I couldn't be happier. People where I play definitely have some upgraded custom guns that out class mine. Also, some stock guns (at least I believe they were stock). But, what I don't have in power and rof (rate of fire) I have made up for with using superior tactics.
Like most people have suggested you should go with an AEG...from my research FPS and barrel length do make a difference some people will tell you these things don't matter. But, you will quickly find they do. If you want to keep open your option of sniping open I would recommend getting an m14 you have a longer barrel which will give you increased accuracy. although that isn't the only thing that affects accuracy it does help. The disadvantage of this would be you are working with a longer platform limiting your mobility. sometimes you need to move fast and having more gun means more things you might bump into with your gun which is never good regardless of how quality your externals are.
I recommend finding a platform you will like. You will find that for the most part I believe they will operate at about the same level just with different life spans depending on the brand you get and how you run your gun different batteries will affect your rof and give your gun more wear. Then look at how easy a specific brand is to upgrade should the need arise. I would suggest looking for things that say TM compatible. In my experience and research it seems as if this is the most common spec'ed type gear box.
In the end I will say I started with a airsoft gun I got about 9 years ago and I found it wasn't so much about the gun (it wasn't great) as much as it was about me learning how the people I played against behaved. It is possible to get kills with a gun that doesn't preform well and have the enemy clueless as to where you are. I'm talking about shooting people 25 feet away and them having no idea where I am even though I am almost totally out in the open. It almost made me feel like a sniper just with out the long range shots.
So, just remember this is just a game. have fun. call your hits. and the gear you run isn't as important as what you can learn from your experiences and how you implement it into the next game.
EDIT: I didn't talk about what you should get...I would say a Classic Army (CA) spartan edition my friend picked one up and is very happy with it. Another, friend got a G&P and is also happy with it, and as I said I got a KWA and am happy with it. I would say the G&P(he got the magpul edition or whatever) seems like it's the hardest to care for...my friend hasn't even removed the barrel to clean it he also had some problems with the hopup not sure if he has solved that or not. The issue with removing the barrel is he didn't want to cut some heat shrink to remove wiring to be able to get deeper into the gun. I believe the CA has the same take down as the KWA which I have found to be very easy to work on although I haven't gone into the gearbox yet.