Stampin' Up! trimmer
I also love my Stampin' Up! trimmer. I have never been able to make such straight cuts. I have not tried the new rotary add on yet, but I plan to. For a trimmer it might be a bit pricey (because there are no coupons) but so far it has been worth EVERY penny. I like that it is portable (basically), the storage compartment underneath keeps track of my extra blades and a few other tools. I still haven't quite figured out the extension arm - meaning it's a little "sticky" trying to pull it out.
I have toyed with the idea of a guillotine cutter but I'm pretty sure I wouldn't use it. Even though I have a dedicated crafting area, my trimmer is moved all over the house. I even take it to work with me sometimes. This trimmer is a little heavier than the other trimmers I have around the house (I have three very crafty daughters).
My vote is to give the SU! trimmer a go unless you're VERY set on having the rotary/guillotine type paper cutter.