I would suggest the software they bundle with is more important these days.
Mine is two years old and plays DVD as well - nice touch I never used. The software is Nero and with version 5.5 it can create VCD - which is a CD that will play as a DVD.
Now if you plan to have it for a few years I think that is a nice compromise between the newish and expenside DVD burners (and the issue or +R, -R or ""£$* R).
Look at the software features first- the burners, for the most part, will do the job and if you don't plan to make CD's for sale the speeds are very much a secondary issue.