Looking at their selection sheets on WBB State...my assessment in bold)
Tulane was 22-10, St. John's 21-10, Villanova 19-13 (advantage Tulane)
RPI - Tulane 50, Villanova 72, St. John's 86. (advantage Tulane)
SOS - Tulane 70, Villanova 71, St. John's 121. (advantage Tulane)
Villanova's 6 top 100 wins are DePaul (RPI 38), Penn (51), NC State (75), St. John's (86), 2x Creighton (87)
Tulane's 5 top 100 wins are AR-Little Rock (32), LSU (55), Miami (62), East Carolina (65), and NC State (75)
St John's 5 top 100 wins are South Florida (26), Seton Hall (40), Villanova (72), 2x Creighton (87).
St. John's has the best win, and two nice top 50 wins but the profiles are all similar...and Tulane didn't get to play Creighton twice.
Tulane has 2 losses to sub-100 teams - Tulsa (111) and Temple (136)
St. John's has 3 losses to sub-100 teams - Butler (141), Indiana State (170), and Xavier (187).
Villanova has 3 losses to sub-100 teams - Butler (141), Sacred Heart (215), and Providence (262).
Villanova has by far the worst losses - to Providence and to Sacred Heart by 23 (at home!)
Overall, I think it's close - the wins and losses don't look that much different to me, but if there's only 1 spot for the three of them, I think Tulane's the logical choice based on RPI and SOS. For the computer lovers (myself included), the Sagarin Ratings are Tulane - 51, Villanova - 59, St. John's 74.