If I had to really break it down.
Sutton is out unless he does something amazing and unheard of in preseason. He doesn't return kicks or do anything else that stands out enough to justify the fifth receiver spot where your actual receiving skills are almost never used.
Campbell has been injured a lot, but he is definitely a deep threat. In 03 and 04 respectively he averaged 20.9 and 19.2 yards per catch on a total of 44 receptions. He also returns kicks in a pinch.
Sam has great size at 6'3 and he played very well over there in Europe. That success might not translate, but he at least has a shot in preseason to do his thing.
Hakim used to be a key part of the greatest show on turf, his speed was electric and his hands were decent at the least. He can return punts/kicks in a pinch, but unlike Campbell it seems his best days are behind him. The last three seasons his yard per catch average has dropped from 17.2 to 14.4 all the way down to 8.6.
I can't say I know much about Reed....but he seems like a long shot at best and the same goes with Malone.
If I had to rank them in order by best chance:
1) Campbell - Speed, Return man, Deep threat.
2) Sam - Size, Played well in Europe
3) Hakim - Speed, Veteran, Return man
4) Sutton - Has promise for the future...just doesnt provide anything this season.
5) Reed/Malone - Long shots.