Even though the rats were probably less maintenence, I prefer guinea pigs. I used to have two female rats. At the time I was only about 10 and we got them from a petstore. The cage absoloutly stank after about 2 days after cleaning them.
Now this is apparently very rare but every time we went to get them out of the cage, they would run and hide. This is pretty common for guinea pigs, although they are very friendly once they are out. The rats would sometimes bite. I have had about 50 guinea pigs altogether and I have never been bitten. Guinea pigs also cost more to look after. But I personally think they are more worth it!