I have all the sizes and use the 45 for cutting out all my pieces and use the 28 when I trim each finished block to size. Have a 60 but rarely use it.

I use either the 45 mm or 60 mm - whichever I find first- or has a sharp blade. I usually only cut one or two layers at a time. So if I make a mistake, it is only one or two layers that have been messed up.

I have 3sizes and use the 60 mm when using the shape cutter. Having a larger blade, it works in the slots best. I can cut 6 layers with it.

I have 18, 28, and 45 mm cutters. I almost always use my 45 mm one. I read somewhere that the 28mm one works best in the shape cutter so I started using that one for the cutter and actually like the cutter now! Although I see that some prefer the 45 or the 60 for the shape cutter.

I have used the 60 at a volunteer event and it worked fine. So it's just a matter of personal preference. I don't usually cut more than 2 layers at a time.

Connie

I use the 60mm almost exclusively lately. I'm not sure if it's the titanium blade or what, but it seems to cut the nicest for most things I cut. It's wonderful for the bulk of a quilt needing to be trimmed, but I use it for 2 layers of quilt cotton too.

I have both but only use the 45 cuz I found the 65 one wobbles too much and I don't get a good cut. just my observation

I have to say, I WOULD use the 60 the most, ( it just seems through fabric easier) but because the blades are MUCH more expensive and Harbor Freight doesn't have inexpensive replacement blades, I use the 45 the most.

I have a 60 mm as well as a couple of 45mm and a very small ones to use with curved rulers. I mainly use the 60mm.
Don't really have a preference it just seems to be close at hands all the time.

It's personal preference and if you have both or several different sizes, it will probably boil down to which one you can find when you are ready to cut. froggyintexas

I use a 45 and own a 28 I seldom have a need for. I have found that for me, the blade size matters less than the type of handle. I bought an ergonomic handle for my 45 mm and I have never looked back. It eliminated the pains I got from the straight handle and I love how the blade cover automatically closes when you release pressure on the handle. If you have never used one, check it out.