Which urchin is best suited?

[fishiefishie]

For my 20g long reef? I had a pencil urchin for quite some time, but just recently passed it along to a friend because I wanted some macroalgae in my tank but it wanted to eat it. (lLttle turkey...I loved him, but really want to try my hand at the macros.)
I am looking at either a pink pincushion or a blue tuxedo. Is either one of those better suited for my tank? Is one hardier than the other?
Oh, and just FYI, by Christmas (prob sooner) I'll be upgrading to a 55g! :dance2:

Thanks!

 

[Amphiprion]

There are only two genera I recommend for your tank size--Mespilia and Echinometra. The former mostly targets coralline algae, whereas the latter would likely be more effective against other algae.