I have both, but mainly use the 45mm because yrs ago, about 30, book subscriptions gave out rotary cutters, and i have the original ones about 4 of them. i have one 60mm, i took from work with me when i quit.

I use a 60 mm for just about everything. I lucked out a few years ago and from Ebay snagged 3 Olfa 60mm stick style cutters, along with a pair of Olfa appliqué scissors, 2 boxes of 3 60mm Olfa replacement blades and a box of 10 Olfa 60mm replacement blades all for $35 including shipping. I gave one of the 60mm cutters and some replacement blades to a friend who quilts. One of the 60mms stays with my big cutting mat that's in another room along with my Sizzix Big Shot Pro.

I have a 45mm Olfa with the ergonomic handle that I sometimes use for quick square ups on the small cutting mat that I keep next to my sewing machine, but I really am more comfortable with the 60mm stick.

Aside from the fact that I prefer the old fashioned stick style cutters over the newer ergonomic ones, I like the 60mm because it just seems to go a little more quickly since the blade is larger and I can cut through 6 to 8 layers of fabric easily and accurately with it.

Rob<object type="cosymantecnisbfw" cotype="cs" id="SILOBFWOBJECTID" style="width: 0px; height: 0px; display: block;"></object>

Like several others above, I also use the 45mm more often than the 60mm. When I use my June Tailor slotted ruler, it works best with the 45mm. I like the Olfa Ergonomic cutters.

I use 45 mm.

What I am cutting also determines the size. When just cutting so I have not so much material to use for cutting specific pieces I use the 60mm. For cutting most pattern pieces I use the 45mm. For cutting curves and yo-yo's I use a much smaller rotary cutter & blade. The purpose defines the use for me.

I am using my 28mm cutter just now for the 365 day challenge as cutting small pieces, I use the 45mm one most of the time and I use the 60mm when when squaring off my quilt sandwich. They all have a different place in my sewing room and I use them all.

I use the 45 most of the time.

My first cutter was a 60mm and I've stuck with it. I bought a 45mm last year because the 60mm blades are so expensive, but I still find the 60mm easier to cut with, even 1 layer--it seems to stay close to the ruler, whereas the 45 tends to veer off. My guess is that a bigger blade's path is more stable than a smaller one.

I use the 45mm for everything---do not even own the 60mm cutter. I did recently buy the smaller one as I may try some curved pieces and have read those are easier with the smaller blade.

I have several of both sizes - it's whichever one seems to be closest to me at the time.