Music Games: Expert
Baldur's Gate-ish RPGs: Easy
The Average Game: Normal
Action RPGs: Hard to Expert.

Most of the time I'll play on normal or hard.

Unless it's a shooter in which case I'll set it to the highest difficulty.

Normal usually. Though with JRPG's I put it on easy cuz grind. I also put DA:O on easy because of the shit console version.

When I was younger, and could go at it all night, I liked everything hard, the harder the better. Even if it made me blow it all and I had to start over again from the beginning, it was still the way I went at it every time.

These days, I know I'll be lucky to even get an hour to do it uninterrupted, so I can't afford to be in a situation where one slip up means losing control. So I take it nice and easy, pacing myself to make steady progress. It isn't as exciting sometimes, but I'll take it how I can get it right now.

On another note, I find I like harder features, even if the difficulty is on Easy. For instance, a hardcore mode that requires keeping up supplies or an Ironman mode that prevents reloading saves makes things very interesting, while not relying on just outright punishing difficulty.

Depends entirely on how hard the game is.

Typically, I prefer the harder difficulties, if only to get a real challenge and improve myself. Some games are easy AF (ME and DA series for example) where even the hard setting isn't exactly challenging and then there are games (think XCom, Galactic Civilizations) that are plenty hard enough on normal or even easy difficulty (especially for players not experienced with their gameplay details).

As a rule of thumb, I play games on hard for the first time and then increase the difficulty for the next playthroughs after I've come familiar with their concepts. For games that are more or less new for me, I use the default settings and then increase the difficulty.

So, long story short: I like it hard.

Usually I start a game with Easy difficulty to learn it. If my first playthrough is medium-normal difficulty, I likely screw it up. When I learn the essentials I'll move to medium difficulty.

Then I go to hardest difficulty if I'm actually able to do it. I'm not content if I die too many times and waste too much time on a mission.
So if there is 1-5 difficulties, I start with 2, then go to 3. Finally into 5.

In general I play most of my game on 3/5 difficulty.