I'd say reaper is easier personally. Your positionals aren't part of your base combo and your base combo is a simple 1-2-3 button press. There's a little more when you unlock demon mode (and it's faster than the normal GCD) but it's not something you have to deal with constantly.

The only thing I don't like about reaper is having to maintain the debuff. The maintenance buffs for sam are a lot more fun to manage because as long as you're doing your combo correctly you maintain them, whenever I have to refresh my debuff on rpr I *always* feel like it's interrupting my rhythm.