Opinions on these? I've been playing through Umbra for my

>>32040960
I'm playing nova. Is very hard. Better than Rising Sun at least.

Imo, you should've played the original SM first, but meh, do as you please.
SM reintroduced gen5 xp mechanics, which means that you gain more xp for beating pokemon above your level, and less for beating pokemon below your level. This helps balance the xp gains with the xp share on, and ensures the league is still challenging.
I only played without the xp share, so I can only talk about that. Most of the time it was easy to keep my mons around trainer level, and most battles were challenging while not being mind-numbing button mashing or too long and stupid. The level curve gets retarded at the start of Poni Island, with the wild pokemon levels being on-par with the last boss fight you have at Aether Paradise, and doesn't stop being retarded up until the league, at which point you're fucked if your mons haven't caught up yet, because there's no good place to grind. Even if you get past the league, you'll have a hard time grinding to get past dexio to reach the first worthwhile grinding spot, at which point you won't even need it anymore.

All in all, SM fixed the difficulty issue of gen6. I would've preferred a smoother level curve, or better grinding spots, but I had fun.
I've gone back and played Yellow on VC, and there's so much wrong with the level curve and battle mechanics I could probably fill a 893x1200 image. It's mind-numbingly easy, even if you skip every possible trainer, as long as you don't get fucked by shit mechanics like wrap.
I should go back and replay Platinum one day, just to compare the difficulty, but I might not be wrong when I say SM is one of the most difficult Pokémon games yet. The level curve is mostly fine, the xp share was fixed, and the AI is top-tier.

>>32040960
I'm having fun with umbra so far, even though the early game difficulty does feel a bit cheap at times (Giga Impact on a level 15 Furret is just silly). Every trainer having items and custom movesets is something I've never seen in a ROM hack before, and it's pretty great; most teams have some sort of gimmick that makes them interesting to battle, instead of just being exp bags.