I like 100mg because I can do the math in my head... each percent of 100mg concentrate equals 1 mg of final mix. So a 100ml mix at 3mg needs 3ml of concentrate. For 10ml it's 0.3ml, and so on.Clo, you'll just use more nic base and less PG than somebody who was using 100mg or 60mg base.
I got the 60mg because my goal is 6mg nic base, and this was the easiest math. 1ml nic base per 10ml juice desired.
A lot of people use 100mg for the same reason.
**EDIT**
With higher nicotine content comes higher danger. Make sure you're wearing gloves when handling ANY nicotine. Be safe!
It's also more space efficient in the freezer when you start stockpiling for the vapocalypse