The retrofit LED trims often look better than an LED bulb installed in a traditional can. Also, I believe that the LED trims often more reliable and include a longer warranty than some of the bulbs. I'm not sure if that's worth the extra money, tough choice!

When we remodeled our kitchen we replaced our 6 inch cans with 4 inch ones but did not increase the number of cans. There was significantly less light from the 4 inch cans because the bulbs are 50 watts and 500 lumens compared to the 75 watt equivelant halogen bulbs with 1,070 lumens that I had in the 6 inch cans. It seemed to me that too much of the light in the 4 inch cans was lost in the can because the par20 bulbs were up high in the can. I had used long neck bulbs in my old 6 inch cans but could not find any long neck Par20 bulbs for the 4 inch cans.
I switched to the LED Retrofit cans because the light is down lower in the can. A par 20 LED bulb would still have been up high in the can like the par20 halogens were. The Retrofit cans that I bought are 600 lumens so I gained a little bit there too. I like not seeing a bulb too. The retrofit cans accomplished what I wanted in my kitchen- more light.
When I get around to changing out my hallway recessed light I will just use LED bulbs because they are 6 inch cans and I don't need to try and squeeze out extra light like I did in my kitchen.