Now some of my fellow sniper said that Arrow rain damage was based from atk% and crossfire was based from crt%, is this true?. If this true, should i focus more on my atk%(AR) or should i focus on crt%(CF) to get the highest dps?
Arrow rain, unless you got hide atk pet skill, doesn't crit. Crossfire does crit. I guess that's what your fellow sniper wanted to say. You should focus more on atk, as after the balance update the formula for critical dmg changed, and you'll get low dmg if you put a lot of crt dmg+%. You can put one critical dmg crysta if you want, but you could even go all atk+%, as cap CRT stat + crt dmg from equips should be enough.
Snipers have 2 skills that adds critical damage as well, so you may want to take that into account when you're building your gear.
hawkeye4 - 25% ambush - 15%
My recommendation for the top-fastkill-solo class will still ultimately be Alchemists due to Damage disable sets and defense-ignoring Ailment damages. It's nigh-impossible for any other class to easily catch up, even with the introduction of Lv360 skills in the far-off future.