As CtM, I found Sec Test Criminals to be my worst matchup, followed by high-link runners, with Whizzard + Slums in 3rd.
The criminals are much, much tougher than whizzard for CtM, particularly if they have any link. High link negates all of the trace effects, including the CtM ID, Resistor (CtM’s best ICE), and any tagging ICE that isn’t Data Raven. Whizzard with Slums can avoid ever triggering the CtM ID, and prevent recursion of important assets/upgrades. This sounds bad, but in most cases, whizzard either falls behind on trashing, and I am able to score out, or he goes broke and I land tags on him (and trash slums).
I don’t think of myself as a top player, but I at least made day 2 at Gencon playing CtM. I beat all 3 on my way there, but the criminals I only beat due to unforced errors.