Urethane grout or epoxy grout is the way to go on countertops. Urethane is easier to work with than epoxy, but epoxy isn't hard- keep most of the mixed grout in the refrigerator until you're ready to use it, it will keep it from setting up. It just takes lots of cleaning, but that's key to any grout job.
Like OLH says, there's more to picking a tile than just porcelain vs. ceramic (and to pick nits, porcelain is ceramic), check for availability of all the sizes/edges you want, check how flat the tiles are (really, it varies a lot), and think about how you're going to cut it- porcelain is harder to cut, and it needs a better saw and blade to keep chips from happening.
I did a kitchen counter with 18 x 18 honed slate and dark gray epoxy grout about 8 years ago, it's a rental house now, but it looks like new still.