WPA pays no attention to defensive contributions, so for a player like Simmons it's not surprising if WAR and WPA differ greatly. Between the two, I would rely less on WPA for assessing "value".
However looking at Simmons's two values in conjunction helps suggest the limits of what a good glove alone can contribute.
For the list of five, I'd go with Colome, Cave, Shoemaker, Astudillo and Happ in some order - is it really important to rank them, with 2 gone and 3 more who should be absent next spring?