Always a quick wave – doesn't matter what kind of cyclist. 50% of the time a 'mornin', or 'alright there' thrown in for good measure too...
Usually, the wave is in the style of a quick hand lift off the bars - in a subtle way, a little like saying 'thank you' to someone when driving. If I'm going hammer and tongs, then that wave may turn into just a finger wave (stretching my fingers / flattening my hand) but still with hand on bar... like saying thank you when driving whilst keeping your hand on the wheel.
Passing a big peloton in the opposite direction I always find tricky... what do you do? Can't be dishing out a wave to everyone, that's a bit too enthusiastic for me. Also a big, single, 20 second wave has freakish undertones too, so I often wave to the front ones and then give a periodic wave as the rest pass... some signal back, half appear a little up themselves or 'busy', even if I recognise them and know that they usually say hi when solo...
Overtaking a cyclist and saying 'hi' is somehow tricky to do right too without coming across as being overly weird or glib.