Speedbooster is Linksys enhancement system to the standard 54mbps "g" speed system. Ultimately many manufacturer's claim an enhancement but what exactly you can get depends very much on your locality. Realistically any wireless systme us an "up to" speed, and frequently you will get less due to distance, reception quality, local interference, blah blah.
I've seen many manufacturer's clami 125mbps. That is realistically "n" standard territory.
Bear in mind your broadband speed maximum is 20mbps. If you have a g standard your broadband will be the limiting factor. If you buy "n" instead of "g" you will have even more in hand.
Linksys is a Cisco brand. That is some assurance on quality given the networking credentials they have. Buffalo could well be perfectly adequate, but they don't have the same brand name kudos.
Earlier versions of the Linksys WRT54GS series could be flashed with third party firmware, but I'm not sure about the current ones. That's why I suggested WRT54GL which is designed to be flashed. Firmware can allow you to boost your signal's amplification which could assist quality if you have thick walls and the like. No idea whether Buffalo stuff can be upgraded this way. I'd do a

and see if there are many reports on issues with people wanting your type of useage especially p2p before I buy.