What type of Engineering?
It'll also depend on the uni, so yes, ask Oxford directly what programs they use and whether you will need to run them outside of computer labs.
In general, the uni will probably provide ample computing facilities so that you won't need to run the programs on your own computer (and this also saves you buying them, engineering programs are VERY expensive)
The uni's computers will also be better suited to running these programs, as they can be very resource hungry, and so you'd need a powerful laptop to run them anyway.
So basically, whatever you prefer the sounds of! I mean, I adore my ThinkPad, but I can see the appeal of Macs, just depends what you think would suit you better!