I use the 45mm blade. I also use the Fiskars handle that is a lot easier on my hands than the upright ones.
I seldom cut more than 4 layers at a time because I find the fabric shifts unless I put a LOT of pressure on my ruler.

I quit making cutting mistakes when I purchased my Altos Quilt Cut.

http://www.quiltcut.com/index.html

I have both. Mostly use 60mm.

have been using both the 45 and the 28 ...... but i tend to get carried away with the larger cutters, and put notches in my fingers ..... specially with the larger blades. have just got an 18mm cutter and gonna give it a try and try saving my fingers. and fingernails. it would probably behoove me to change my hold on the ruler, though

Do any of you who have orders for blades from Harbor Freight that are on backorder received them yet? I haven't. I just emailed them to ask about it though.

i have 3 sizes..use the 45mm the most. the 60mm,i use when working with fleece. i still don't cut anymore than 4 layers at a time.

the 60mm cutter is good for cutting thicker/heavier fabrics, like layers of flannel; the little dips you get when you cut folded fabric is from your fabric not being folded straight
it may 'seem' straight but if it is not on-grain (the salvage edges are not always straight and should not be used to square up, the salvages should be removed, then square up the fabric using the fold as your straight edge making sure everything is straight and you will not get little v's in your cut edges even if you have 3 or 4 folds.

That is what I do. My mat is long enough (24 inches) that I only have one fold. I iron that crisp, and make sure that my ruler is lined up along that fold. I also check about every 5-6 cuts to make sure the edge is still straight with the fold, and re-square as needed. It makes a big difference.

Boy did I learn a lesson (the hard way), cutting strips for my log cabin 1 1/2 inch. Got tired and cut 6 layers at a time. Hope they all fit

The little dips have more to do with the folding than the cutting.

When the directions say to fold selvage to selvage - I fold it so there are no diagonal folds/creases/pulls in the fabric - so sometimes the ends are very uneven. Washing frequently lets fabric "relax" a bit and do its own thing. Sometimes fabric gets skewed while being processed.