I have the June Tailor 12" and really liked it but I subsequently bought the Stripology ruler. If I were going to invest I definitely would go with the Stripology ruler as it is more versatile. Just my suggestion.

I had the 12 inch for years before investing in the 18 inch. I love my 18 inch one, but storage isn't a problem for me, it fits in my ruler rack. I got my big one with a coupon at JAF, but they only sell it online.

I have the largest one and love it!

I have the 12 x 12 and use it more than I use rulers. Having the 18" would be nice, but not really necessary. Besides cutting strips, I've used mine to sub cut blocks and to trim/square blocks.

I have the 12 X 18 and I love it.
I used it to cut all my fabric.

I love the 12 x 12. The 12 x 18 is too floppy for me

I have the 12x12" one. The 12x18" was too expensive for me. It works fine for me. Just make sure you have either a 45mm or 60mm rotary cutter as I found the 28mm I had didn't cut properly with the ShapeCut.

I have several June Taylor slotted rulers and use them constantly. My favorite is the one that I use for cutting 2 1/2" strips. I have two of the ones that have half inch markings. I use them every time I cut fabric. I use painters tape slivers to mark where I want to cut ( e.g., every 4"). I also have one that is marked every fourth of an inch. It is a small ruler; but I use it often. Finally, I have her ruler that measures eighths. Today, I had to cut lots of 2 7/8" squares. The ruler was a life saver! I have an electric Accuquilt Go and lots of dies; but I find that I do most of my cutting using June Taylbor slotted rulers. I love them!

I like the larger one better, can cut more without repositioning

I have both the 12" and the 18". I find I use the 18" more often but it's just a matter of convenience. You can, obviously, cut more strips before you have to move the ruler. I used the 12" for many years before I found the 18" and I still use it when I don't need the full 18".