It depends on your personal objectives. The roll rate should be whatever you can comfortably stop at the 180 or 360 degree mark. Faster rolls will require less correction of elevator and rudder, slower rolls can be more accurate, but only within your ability to coordinate elevator and rudder.

If you're competing in your first season, my advice would be to use the fastest roll rate you can bring to a quick stop on the half roll or full roll mark, or within a very few degrees of wings perfectly level. That might be about one second for a full roll. You should get by fairly well with just a blip of elevator correction at the half-roll mark--IF your roll rate is not too fast, not too slow. Don't forget, a consistent roll rate depends on a consistent airspeed of your model, so practice your upwind and downwind cruising speeds at a consistent rate, level and diagonal up & down. So much to keep track of! Practice is the only solution. A little advice now and then can help, but only if you practice.

A very good exercise for timing the push-elevator input at the 180 mark is to do linked rolls--two rolls, three rolls, four rolls, as many as you can do, continuous rotation, no pauses, keeping a straight & level track or as close as you can come to it. This will teach you timing, rhythm and how small a blip of elevator it takes to keep you on axis. Also, don't overlook the half roll on reverse Cubans where you catch the tail with a little push elevator when you come inverted, keep that 45 degree upline nice and straight. Then gently release that push to transition into the pulled loop segment.

I remember my coach telling me he would do the linked rolls exercise endlessly at his field, and when his timing was a little off he would find himself doing rolling circles. The peanut gallery would give him plaudits for doing rolling circles, but he said what they didn't know was that the rolling circle stuff was easy, the straight and axial linked rolls were the hard part.

I remember in my first season using rudder correction for half rolls, as in the two of two-point, Cubans, Immelmanns, etc.--opposite rudder rolling from upright, same rudder rolling from inverted. It was easier for me to use just one stroke of rudder input for a half roll, whereas <opposite rudder/push/same rudder/pull> was a bit much for a non-slow roll. There was a period when I was practicing slow rolls where it was easier for me to do an on-axis slow roll than it was to do a standard roll.