I use both sizes, the larger for straight cuts and smaller diameter for cutting tight curves. I think the larger is easier to control and of course, gives you more mileage for your motion since diameter is larger. The smaller is needed to fit in the tighter curves of template but can work for both if you only want one. I don't know what size my small one is.

I just use my regular cutter for PP (45mm). I have a 'Add a quarter' ruler that I use to trim seams to a 1/4" and the small cutter (18mm) doesn't work with the ruler. The 25mm may work with the ruler, but I don't know for sure.
Having a small cutting mat at the sewing machine works well. I think my small mat is about 5"X7". Saves having to get up after every seam to trim.
Cathy

Here is a link that might be useful: Add-A-Quarter Rulers

I bought a set of Omnigrid Marking Ruler Trio - for adding a quarter - they specifically say not to use with rotary cutters. Live and learn - They are only good for drawing a 1/4" line such as for HST - I never would have bought them had I realized I can't use them w/ the rotary cutter.

I am using a 12" mat that turns next to the machine, and I am waiting for delivery of a small iron that Gwen ( sunnycentralfl) recommended.

I'm really on the fence about buying the smaller cutter.

Here is a link that might be useful: Small iron Gwen recommended

For what it's worth, I've always used a larger cutter when paper piecing (45 mm or 60 mm) and it has never been an issue. I don't have an add-a-quarter ruler, I just usually use my 6.5 x 6.5 ruler to add a quarter that way.

Lola

Convinced - I'll save my money & continue to use my 45mm cutter. Thanks!

I've always used my 45mm cutter for all work including all paper piecing. I think the 'Add-a-Quarter' is virtually a must have for pp. It makes things so, so much easier!

I have a 18mm cutter that I almost never use... It is good for cutting around circle templates, but that's about it for me.

I don't own a 60mm and the only time I've needed it was with my kaleidescope quilt when cutting through so many layers of fabric. I was in a class and just borrowed one.

I use the 45mm cutter for almost everything. I do have the smaller cutter, but unless I'm cutting out a clothing pattern, I find it "fussy". It is good for tight curves, but I don't cut them often enough to make it worthwhile to have them both.

Thank you Jennifer and Mary. I just finished a PP Multi Faceted Star - alot of pieces and seams, and I see that a smaller cutter would not have cut thru all the multiple pieces. I could have used a larger cutter when I made my Stack n Whack.
Jennifer - I am using a EZ Companion Angle ruler - it is a triangle - I don't know how to use it for its intended purpose, but it is working great so far. I am going to look at the "Add a Qtr" since I like PPing.

I'm doing the Sylvia's Bridal Sampler quilt with an internet group. This week's block required the dreaded PP technique, which always makes my brain hurt.

I used a small rotary cutter and mat placed next to my machine figuring it would make the process go more smoothly. Took me the first seam to realize I still had to iron each time. Sigh.

That small cutter did take some getting used to and I'm not entirely sure if I like it or not.

Close to three hours later I had completed a 6" square.

Dianne