All the ceiling cans I've ever had allow you to adjust the bulb height so that you can have the bulb be flush with the ceiling, or recessed an inch or two, or recessed very far up (maybe up to 6" or so, I'm not sure). You can just experiment with the adjustability and see which height you like.

A more essential question when choosing can trim is the color of the baffle (the inside lining of the can that you can see when you look up at the can). Many interior designers like black, because there is less glare. That's true, but I myself don't like black baffles, because during the day, when the lights are off, you have a ceiling full of black holes. White baffles will disappear more into your ceiling, but can cause glare. I have white baffles in my ceiling and I like them. But if I had more of a budget, the best baffle, IMHO, is called "specular" or "Alzak", a silvery color. It pretty much disappears or has an attractive silvery-ness during the day, and reflects the light really well. "Haze Alzak" from Juno is said to have less glare than "clear Alzak". The downside is the cost, much more than white or black trim, and if you have a lot of cans, it can really add up. Also, sometimes it is hard to know whether you are getting "Alzak", as different manufacturers call it different things. Juno calls it Alzak, Halo calls it "specular", and I don't know what Lightolier calls it. But, just something to think about.