Which is more safer and easier to play to end game content and also able learn/have easiest time doing contents ?
I would think SH cause the main issue with artillerist id the ability delay. You need a good grip of boss mechs to pull off artillerist well imo. I love my alt though chaos is really quick with artillerist. Dying from or missing a boss from animation lock/or delay can feel bad though. I hear SH is one of the best classes to familiarize yourself with endgame ;). Both are fun
My SH is at 993, and despite I consider myself a movement legastenic, it is alot of fun to play.
I went all crit+specialist with demonic impulse.
As Toadsmoke mentioned, occasionaly one missed the boss anyway.
After some testplaying to ilvl 90, then I used the PowerPass on the Artilerist.
So far my experience with Chaos, Guardian and Abyss is: Slow, miss often - until my attack arrives, mobs/demi-boss is either down or moved away.
Still feels fun to play though - Me needs some more practice 
Play blade, has great mobility and positioning. Puts out similar if not higher numbers than shadowhunter too. Arty has decent movement with high swiftness but some skills can be tricky to land, they aren’t instantaneous.