Great question, I have 2 bought cages, one has glass on two sides and wood on the ends, The other is 4 sides of perspex. I think in all honesty it is probably better for the hamster to have a totally dark place to sleep (although some will sleep out in the open, or squashed up in corners against the glass/perspex). They are all different.
My syrian Twinkle who is in the 4 sided perspex cage has his house up against one corner and i did see his food stash at one time underneath the house so I could watch him sleep eat, but I didn't see him sleep. So whatever you end up doing your hamster may have it's own idea whether you see what he gets up to or not.
So, I guess it's entirely up to you really and what you prefer to do.
