Although both BuffaloTech and Linksys' cards are essentially the same Broadcom hardware design, their firmware and drivers are different. My testing of both products so far shows significantly different performance, with neither card coming out solidly ahead.
If you buy now, you'll be depending on the company you choose to support you through their (and Broadcom's) learning curve, and to also make sure that the draft-802.11g product you buy turns into a released 802.11g-compatible product toward the middle of this year.
Fortunately, both companies have clear positions on this subject with BuffaloTech saying that their draft-802.11g products will be compatible or they will fix or replace them, while Linksys says they "cannot guarantee compatibility with a standard that is not official". 'Nuff said!