Just got back from Barcelona...we didn't go to Cal Pep either, coz it sounded too touristy. We loved Paco Meralgo...food was mostly excellent...there were some tourists, but I would say mostly locals. I got the feeling from the waiter that he is not thrilled with the tourist crowd - or maybe he was just having a bad day...but it was a fun evening and the food is defintely worth a repeat visit.
I haven't been to Cal Pep in almost three years so I can't speak to its current quality. I had dinner at Paco last night though and enjoyed it a lot. I think both places serve very high quality food.
My problem with Pep is that it is always very crowded and has become a bit of a tourist destination. Paco, while busy, is not as crowded and is less touristy (you get to rub shoulders with the 30-something yuppies of the Eixample). You are not squeezed along a bar with a line of people looking over your shoulder waiting for you to hurry up and finish your food as you are at Cal Pep.
In terms of food, there is more variety at Paco--you can get the same fried fish and grilled shellfish that Cap Pep serves, and you can also get salads, steaks, croquettes, ragouts, etc. Although, I have to say that the tortilla with the hidden pieces of chorizo at Cal Pep makes it worth the trip.