I've seen different widths in the same block (barnbum) that are fabulous!! It's really up to you.
If hand quilting I wouldn't go smaller than 2 inches wide just b/c of all the seams.

Thanks everyone!

I'm doing a 2 1/2" log cabin now, but I don't like it. JMHO, the logs are too wide, but my strips are cut so I'll finish.

I use 1-1/2" for smaller quilts, either 2 or 2-1/2" if I want to make a king size bed quilt.

I personally like the smaller strips. I start with 1 1/2 inch strips.

I like the smaller strips for scrappy , it helps the colors blend together better. I typically use 1.5 strips for scrappy. I have done some with 1.25 . If you want a bit curvy , either the dark or the light needs to be smaller strips , I did 1.5 for the dark and 1.25 for the light.

I almost always use 1.5" strips, making 1" finished logs. I find that scrappy fabrics go together better when they're cut into smaller widths, and I like to have more blocks so I can make more complex designs.

I just saw an add in the May/June issue of Fons & Porter's Love of Quilting:

Make Log Cabin Blocks Quick, Easy & SQUARE. A book by Marti Michell.

6 different width of strips, all size of quilts. Sounds like a good book. I may have to get it.

I'm working on reproducing a vintage Log Cabin that uses 6.5" centers and 2.75" strips: From Patchwork by Diana Lodge

I use any size from 1.5 in to 3 in depending on my mood or size of the quilt. on a queen I use 2.5 or 3 in on smaller quilts I use narrower strips.