That is it really! I am currently weighing up the pros and cons of each. I have had both, but had the guinea pigs when I was very young and we never let them have the run of the garden as there were far to many places to lose them.
I now have a small and completely fenced in garden, which would be ideal for either to run around in, but I am not keen on having all the plants in my garden decimated rabbit style and was wondering if guinea pigs are a bit less destructive?