Chances are they were probably ECC83S's.
I don't mean to say they sound bad! I like them better than most, especially for high-gain, and they have been solidly reliably to me, but not everyone agrees. Tubes tend to be a topic that people are pretty radical about. I don't think replacing the tubes completely changes the way an amp sound. If it's an open-sounding amp to begin with, no amount of ECC83S's can change that, lol. You will notice a varying amount of "open-sounding" as well bassy, trebly, distorted, clean, etc. if you try different brands and models, though.
I tend to like plain-jane tubes, personally, but my amps are pretty far from being Fender HRD's, so I don't know what to recommend for that. I think experimenting with tubes is your best bet. Doug at Doug tubes sells a set so that you can swap a couple of the most popular tubes in a few different spots to see which you like best. I'm sure other people sell these "tube cocktails" as well.