Martha Stewart punches are my absolute favorite, especially the around the page border ones. They punch very smoothly and make beautiful, clean cuts. I know others like the EK success ones and the Lucky 8 punches (which are HUGE) are also popular.
Think about what you want to use the punches for and how you will store them. Like all supplies, they can become very addictive once you get started, so build your stash slowly and use coupons.