"Best" is a difficult word to use in this game
That being said, are you using the term "ranged assassin" to mean"ranged" rogue? Just checking for clarity.
Here's a decent to Level 5 base for a Ranged Rogue.
Start:
You start the game with 4 trait points:
Raise Agility to 2 (takes 3 points): Gives +2 to range/light attack and +2 for defense
Raise Awareness to 1 (takes 1 point): sets up for level gain, gives some detection, sets up for better result of Seeds of Trust Quest.
You start the game with 1 skill point:
Learn skill Sprint: sprint is very useful for ranged attackers and traveling
Level 2
Raise Awareness to 2 (takes 2 points): gets +1 to ranged attack
Learn Evasion I (takes 1 point): 50% dodge, helps stay alive.
Learn Archery I: +1 range, stun chance.
Level 3
Raise Endurance to 1 (takes 1 point): Extra HP
Raise Intellect to 1 (takes 1 point): XP gain, sets up for next level gain
Raise Archery I to Archery II (takes 2 points): range damage and stun chance
Level 4
Raise Personalty to 1 (takes 1 point): Gossip, plus some elemental protection)
Save 1 Trait point and both skill points unless already have Ancient Tolassian Tomes, than Raise Intellect to 2 (takes 2 points).
Level 5
Save Trait points, unless already have Ancient Tolassian Tome, than Raise Agility to 3.
Raise Archery II to Archer III (takes 3 points): range damage and stun chance
At this point you should have 1 skill point in reserve. You can either use it for a skill or keep it in reserve until Advanced Skills can be learned. One option is to save enough skill points to allow heavy investing in Advanced Skills Precision Shots, Rapid Fire, Poison Master.
Here's a Youtube video of one Archer build wiping out the orc lair (not my video).
https://www.youtube.com/watch?v=bInSG-IehPw