doesnt matter what map, learn to lash with both, but this thread is about the Adept not the Vanguard, no wonder threads get locked when you cant stay on topic 
I used to always put lash into both. Then on PS3 with new manifest and it opening my eyes to more power style, and as I was playing with these kits more, I noticed;
I'd rather have the Vanguard more buff tanky with full fitness instead, and play him as a pure close quarter kit. And try to adjust this play style to work on any map or part of a map. So pugging with him always felt fresh and new learning experience (especially on the Terminator pipe). Basically became a game of it's own, and why I like this kit so much now compared to not getting him at all before.
The Adept having lash makes more sense because he can't close ground as fast as Vanguard (who should always be in CQ range no matter what), so the distant detonation come in handy for the Adept.