Hey there Pattalutt.
I can't really say what's harder - depends what you are used to and what comp you play.
It's also quite different healing vs dpsing.
I would say the hardest is Disc, because "basically" in shadowform you dot up everything and watch it die slowly.
You might not have good partners or your synergy might not be good enough, just keep practicing and it'll come in time.
You are more than welcome to tell me what setup you currently play or what setup you could play as shadow, and I'll gladly give you some tips vs specific comps or situations.
If you want a clean advice on your question, yes go try shadow, you will love it for sure, and the skillcap is much lower than disc
Good luck