Digital BW, The Print

I often create sheets of many small images (6 5x5's on a 11x17 sheet) but I need a 
good idiot proof paper cutter so I can get good even cuts.  I've been using a ruler and 
xacto knife but I can't say that the results have been great.  All the local places don't 
have a good selection of paper cutters and I'm not sure what to look for.

Should I get a guillotine type or another type (the kind with the blade that you move 
back and forth... not sure what they are called though)

Any recommendations on quality brands and things to look for would be appreciated.

Thanks,
Jeff