After the loss of Richard Marshall to Miami the Cardinals were expected to look for someone to come in. Jarret Bush was formerly of the Packers but mainly in the reserve role for his six year career, sort of like our Money Mike Adams. Over his six year career he has acquired 3 INT's, 22 Pass Deflections, 1.5 Sacks, and 130 Total Tackles. His versatility to play both Strong Safety and Corner is what appears to be drawing interest by the Cardinals.
William Gay on the other was in a reserve role his previous 4 years, until acquiring the starting position this year for the Pittsburgh Steelers. He has similar stats to Bush, racking up 3 INT's, 43 Pass Deflections, 2 FF's, 3.0 Sacks, and 247 total tackles. Similarly to Bush he can also play both the Corner spot and both Safety Positions.
I would personally take Gay over Bush, mainly for his ability to play at both safety positions, and his starting experience, as well as he knows the system that Ray Horton runs. It'll be interesting to see if one of these two are signed, or if they drop off the radar like Bell did.