I would go the roku (unless they are really big into music). For looks/design the apple was better then the first three generations of the roku. With the fourth generation roku (even tho it is called the roku 2) they are about the same looking now (roku a little smaller now then the apple).
The apples remote still seems more solid. You are right tho, while it is sleek looking it is rather small. The roku is bigger, and while not feeling as solid, it does nice as well. The new remotes on the roku are blue tooth, while the apple is still IR. This means it needs line of sight to work. With the roku you can in theory hide the device in back & the remote would still work.
TV Connection Options: This has always been one of apples short comings. If you do not have an open hdmi port, there is really not much else to do. Roku still supports older TV's better, or those with a single hdmi in use. The apple still does have the digital optical out (which is nice). Roku no longer has it. You would have to try and find a new roku xds model online (which is roku's best model even tho it is not the newest).
USB Interface: The apple's usb is really only for show. It does very little other then connect for itunes. With the roku's usb you can connect a thumb drive or external hard drive to it. Then watch movies, listen to music, or view pictures. The formats are still limited, but it is a work in progress. I would avoid thumb drives or anything that does not have a power source. It takes for ever to load.
Wireless network: They are about the same. The roku did add the n/g to the newer models, You still have to find the sweet spot for it tho.
Interface Animated Menus: Once on and working, the apple has a better user interface. The roku is still very basic but strait forward. Seems there are more steps needed to do the same thing tho. The apple's just looks nicer and seems to flow better.
Viewing Content: The roku wins this one hands down. There are many more things to watch on the roku then the apple.
Music: The roku does not have itunes. If you want music and lots of it, the apple is the way to go.
Price: About the same
All said and done, I would say the roku is the better choice for them.