I'm slowly putting together a master set. There are 36 different card fronts, the master set totals 114 cards with the different front/back combinations. I have 65 different so far, 57% complete.
I tried to find a complete checklist to post but couldn't. The checklist I use of course only shows the cards I need. I think I pulled the complete checklist from the PSA site which showed which front back combinations were more scarce. Of course knowing which front/back combos are rare is must have information, hopefully somebody else has a checklist.
My recent focus has been on other parts of my collection, so it's been awhile since I thumbed through these. I do not yet even have a "basic" set of 36 cards since I need Cochrane/Kamm/Ruel/Simmons.
I own two of the four Babe Ruth cards, both of these have rare backs. The two I need (1J and 3A backs) are common backs.