I thought I'd already replied to this thread. Is it a duplicate of an older one that dropped off the radar?
Oh well, sorry if I'm repeating myself, but:
I still like Regent mostly. Regent is what the game classes as "normal", so playing less feels like I'm not playing properly and playing higher feels like pointless self-masochism. And for my style of play, Regent offers me everything I want from the game, that is, the building aspect. I basically treat the game like a building sim/game where the AI's job is to provide a sort of Barbarian-like hindrance rather than the threat of a game-over. Just something to keep me on my toes and push me a bit harder than simply building all-Workers.
Unfortunately, Regent can seem a tad too easy at times and it's a bit harder to motivate one's self to keep at it when it gets to the pressing end-turn a lot in the latter stages of the game, but I've found I still prefer this kind of repetitive action to the even more tedious repetition of cleaning 20 pollution squares every turn or firing 100 artillery rounds every turn. So occasionally I've dipped into Monarch and Emperor for some more intense victories, but I usually revert back to Regent for my normal preferred pace. I even like to go for a Sid every now and then, reload until I start alone on a small island, fill all my coastal-border squares with one warrior, then click end-turn until an AI gets some random victory, but just to remind me why I prefer Regent really.
I'd say 70% Regent, 10% Monarch, 19% Emperor and 1% Sid.