A great question asked and a dilemma I haven't been able to come up with an exact answer to...
I think Davis has a better skill set, jumper if falling is nice, good passer, plays better team defense AND can defend some centers due to his unique body. Some say he's fat but the man is just a big guy, look at his form, legs, chest compared to perk.
Leon I love, sort of guy I'd keep on my team as a bench player for his entire career. He knows his job and simply outworks a huge % of nba players, subs or starters. If he was 6'9"

I think no matter who would be the "one" to stay my opinion is either guy is trade bait. Much like Pruitt who can look good as a backup to rondo but we don't really need a young pg and a young backup. If a good trade comes up and leon is part of it, I'd say he's gone...likewise with davis. Davis did cry after kg yelled at him, big negative in my book.
A good thing to throw into argument; right now can Powe start for an nba team as pf? I feel he could start for some of the lesser teams needing a banger. Could Davis start right now for anyone in league, I don't think so.
Sign both go from there, trade or otherwise.