jg bar 10 no question, it comes stock like 430 fps, it is a farely cheap gun, it is a copy of the vsr 10, which costs about 900 dollars, so you save a lot with the jg version around 800 dollars less. it is also the most highly upgradable gun, the recommended max upgrade, will bring you to about 600 fps, but they do make more powerful springs, but you run the risk of your gun breaking. it is a very reliable gun, bolt action, you can order on off of airsoftgi.com, that's where i got mine.
UTG Shadow ops airsoft sniper rifle (L96 Type 96)
m14
The one you can afford.
Buy a decent sniper rifle (gas or spring) a scope if it doesn't come with one and then practice.
try evike.com
The one that you shoot the best.
"Best" requires opinion, "sniper" refers to how you use it, and "cheap" descries the user. Airsoft is a manufacturer. Please respect this site as the privilege that it is or risk blockage.
Into the clip or magazine on the underside of the rifle, in front of the trigger
Your Madre on un toastio
Yes. You can get replacement springs for airsoft sniper rifles.
No.
you will never go wrong if you buy the best you can afford