I'd argue the min MN chain should be at least 4 long.
Assuming (with medium paranoia settings) that the "bad guy" has a handle on 10%-20% of MN's (100-250 nodes), then with a 2 MN chain length the above numbers predict between a 1%-4% chance of a de-anonymization. This is far too high IMO.
There should be no option to select rounds... it should be 8 minimum with those that want added mixing to go above that. With no fees per round, it makes sense not to have less anon'd coins (those in which the user chooses less than 8 rounds).