I would either go for a a longer G36K or an M4 variant with a standard length barrel and avoid any CQB type lengths of barrels if you want a longer, more stable shot.

Dude, wait for age verification, then look for the little boxes.

Until then, consider an M16 if you plan on long range engagements (with no plans for CQB/CQC). MP5's can offer alot of good things aswell, but really all round goodness tend to come in the G36 package.