The only way to know is to test. The number to look at is the recurring revenue/average income per member.
While it is true that you may find that $29.95 converts just as well as $19.95, or possibly even gets more joins, the retention may differ drastically, so keeping an eye on the retention is key.
Certainly if you can keep a person paying at the lower price for a year vs the higher price at only 45 to 60 days, then the lower price would make you more. So maybe you set the higher price for joins but keep the lower price for recurring, but only by testing will you know what works best.
