Although I went with Mech, after reading the thread... I can't decide. Most likely I'd go mechanical with some Bio. For specifics, I'd get a mechanical arm with a hidden blade while on the Bio end I'd fix my eyes (short sightedness sucks) and strengthen my internal organs.
Also, here is some other stuff.
Firstly, to those that say Mech will survive longer the Bio, I find that statement to be flawed. It is possible to via Bio engineering extend the natural lifespan of a living creature, human or otherwise. I don't know how as my knowledge of internal organs, DNA etc. is comparable to a rock's perception of the world but I do know that it can happen and probably will happen.
Secondly, Wintermute_, something Bio engineering has over Mechanical augmentation is surprise. If you look at a mechanically augmented person, unless the changes are on the inside, your going to more or less know what they have done while with a Bio engineered person, your not going to know if they made they eyes sharper or given their arm the ability to change into some bio-cannon that could level a block. This could also be a disadvantage in the design phase (Mech: Know what your doing from the get-go. Bio: Testing the waters to see what happens).
Thirdly, to those who said HUD, I'd just prefer them as part of a pair of sunglasses. I'll skip some random rant and and just say HUD + Sunglasses = deadly pair of shades.
Lastly; Having played Frac/ture long ago, while the game was meh, the Biological augmentations people had were interesting.