So I have a Shai and a Lahn and can't decide which to main. Im only interested in PVE/Lifeskill so I know Shai have a bonus at lifeskilling like Pro1 Alchemy and a boost on LT but I feel Lahn do a more quick mob grind so Im between them. I already test both and I love Lahn fly perk but maybe im wrong but I feel shai can do lifeskilling faster. Any opinions?

Why dont you just tag Shai and Lahn together? That way you can profit from the speed of Lahn grinding, and also just do lifeskilling with your shai.

Thought about it but I like 1 class to do everything. Been like that on every MMO.

Then I would recommend Lahn. You can keep the shai around, but the lahn is simply better at grinding and her superior mobility is also good for gathering. The additional weight and life exp is good for cooking and alchemy, which i would recommend using an alt char for, for multiple reasons (ressource management, positioning, imperial turnins, inventory space / weight, life skill buffs). But overall for combat, other than specific group grind spots, Lahn is simply better than Shai.