*****,
Obviously the decision is ultimately yours, but I've done a bit of research on this (including asking cyclists I know) and there seems to be a very definite preference amongst cyclists for the hoop-type stands that I've specified.
Firstly, the wall bracket type can buckle the front wheel if the bike gets knocked around and for this reason many people won't use these. Secondly, cyclists much prefer the hoop type system because you can use a proper D-lock to secure both the frame and the wheel(s).
A couple of people have told me that their workplace provides those wall-bracket types but they prefer not to use them and lock their bike to a railing outside instead.
Have a look here:
http://olybikes.blogspot.com/2006/12/ok-i-suck-but-bad-bike-racks-suck.html
Also, as far as I can see, using the wall brackets wouldn't actually allow you to store any more bikes in that space than the floor-mounted hoops - I think it's a bit of a myth that they are more efficient.
Let me know what you think -
****.