What is the monthly premium?
You should pick a plan with a monthly premium that you can afford to the best of your ability. This is key because you must pay this amount every month whether you use the plan or not.
If you only go to the doctor on average of once or twice a year, do not pick a plan that is more expensive because it has unlimited doctor visits. Keep your fixed costs down by choosing a plan that has a few doctors visits per year at a fixed rate.