I had the pleasure of trying the gelato at San Crispino (Pantheon location) and at Giolitti on a recent trip to Rome. Giolitti had my favorite flavor of the trip--caramelized fig, which was insanely good. I also didn't mind that they top your cone with a big dollop of whipped cream.
I went to San Crispino twice. I love the blackboard with flavor combination suggestions and I tried two of the combinations, lemon and pistachio (both great) and chocolate and licorice (chocolate was nothing special, but the licorice flavor was excellent)
I look forward to returning to Rome to conduct a more thorough search for the best gelato flavors in the city :)