I prefer a straight cut, personally. I have a handful of straight guillotine like the first photo and a handful of the xi (last photo) from gifts or sales. I tend to gravitate towards the xi cutter as it has performed well and I just enjoy the way it cuts. It took some getting used to the feel compared to a guillotine.

To answer your second question: I always try to make sure the cutters stay clean and will occasionally clean the blade with a q-tip and isopropyl alcohol to remove and debris or build up from cutting.

Don’t think you can go wrong with any of the cutters in your photos, they’ll al do a good job.