1) Shadow is more of an hybrid class. You do get nice Force Powers, but you don't get saber moves as cool as Sentinels.
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Pvp
2) I play hybrid - tanky in PVP so I can't say if it can compare damage wise, of course it can't with my build, but I usually dish out pretty good damage, it doesn't feel boring or bad, with the added survivability it's pretty fun
3) Gotta love that execute, it just amazing. You have CD's to escape a fight if needed, and many buffs to survive through fights.
4) As a Tanky Shadow I never fear any 1v1 from anyone, I've often won 2v1 also.
5) I'd pick both and that's why I'm getting a Sentinel to 50 also. Shadow's already 50
Regardless, you don't need these answers. You just try out both and see what seems to be more fun
I love my shadow's tankiness, and I also love my sentinel (32 atm)'s damage and burst.
I hope I was helpful.