I use the 60 for several layers of fabric or repeated long cuts. My workhorse is the 45 I use it the most and the 28 for paperpiecing.

I use my 45 mm almost always. Have a 28 mm for small stuff.
Don't use a 60 mm, as they are too big and a bit unruly. JMHO~

I have all sizes. Usually use the 45mm for most cutting, the 28mm for PaperPiecing trimming and the 60mm for thicker layers of batting or fleece. I personally don't like to cut more than about 6 layers so the 45mm works best most of the time. The very smallest (18mm) cutter I only have used a couple of times for cutting smaller curves.

Would 60 be better used for fleece?

I use a 45 have not tried 60 but generally do not cut thick fabric or more than 6-8 layer of fabric at a time. 45 has alwasys worked well for me. I have q 28 and rarely use it, but do not cut many curved pieces.

if you want to get replacement blades from harbor freight, they fit the 45.
i use the 28 for curves

I use my 60mm Olfa more than any of the rest.

I only have a 60mm and I like it, but I put a 45mm & 28mm on my Christmas list. Can't have too many rotary cutters, right? The 60 does go thru several layers well and is good for fleece.

I have used both but I tend to grab the 60mm first. Just my preference...

I used to use the 45 mm as my primary cutter, however, as I have aged and gotten a few wrist and hand issues, I find the 60mm is easier for longer periods of time. I use the small blades (20 something mm) for paper piecing on a small mat at my machine.