It looks like they have similar components but I’d go with the lefty based on the fact that it has a 29er option and comes with the ever popular 1X. That is without regard to suspension however which might change things for me.
Are you doing XC racing? The FSI is a pretty sweet race bike and an awesome spec (the cranks, fork & wheelset are awesome.) It’s comfortable for a race bike with the Save stays, etc. but if you weren’t planning on racing there are better options. If you’re doing trail riding the Habit is pretty nice, although it’s pretty heavy. My hardtail is pretty burly and it’s about 4-5 lbs lighter than my much wife’s much smaller 1x carbon habit. But with a 2×11 and a nice frame/rear shock that Habit would be prime for upgrading down the way too.