I think you're looking solely at design here. Either, installed in sufficient numbers, will provide ample light.

I'd say 6" look a little more traditional. 4" look a little more contemporary. You can get reflector (modern looking) or diffuser (traditional looking) lights in either size.

The 4" will generally put out up to around 575 lumens each. The 6" can put out over 800 lumens, so you might need fewer if larger.

Personally, I think of the smaller ones as more of accent fixtures. Like if you had a painting, you might put two fancy 4" gimballs highlighting it. For general lighting, where you're not meant to see the lighting as a feature rather just enjoy the room for being well lit I'd go with david and put in larger.

But nothing would be wrong w smaller too if that's your design.

Go to houzz.com, search for "recessed lighting" and see what jumps out at you.

-mike

I went with the CR6 primarily because my home already had 6" cans and the CR4 wasn't available then. The 4" LR4 was cost prohibitive compared with the LR6 and subsequent CR6.

If I had to do all the recessed lighting again using cans (same ceiling height, cost is not a consideration), I'd probably choose 4".

6" can advantages
1. easier to change out lamps. The socket inside 4" Halo cans is difficult to access if you have big hands and you're trying to install a CR4.
2. cheaper.
3. potentially better light spread (using traditional lamps).

4" can advantages
1. smaller circumference to seal off.
2. better looking (if you prefer smaller holes)

Do the cost calculation and decide if the added expense is worth it.

I agree with both of the prior posts. Smaller holes are nice, but lean more contemporary. If you need too many of them, I think that can be more of the landing strip look folks like to avoid. Fewer larger holes are what I have in most of my more traditional home. You need fewer and the cost for each is less. Go figure.

Six-inch cans also allow the option of using higher lumen LEDs at a higher cost if desired. I used a mixture of 575 lm and 800 lm six-inch LEDs, with the brighter LEDs being used over the island and over the kitchen sink.

Thank you - I am leaning towards the 4" based on this information but will now be able to ask the electrician some cost questions!