Bang for buck I'd say udp. Gears will lower your mileage if you do allot of highway driving, maybe help if you live in a city. If you plan serious things in the future then a tuner would be good too. It would help to know your goals and driving style. Straight line accel? carving corners? And a budget too. I like carving so I aim less engine more suspension. A t-loc would serve both for you and most of the time I can get them in right without removing the pinion (or I've just been lucky) so long as the same gears are going back in. I got one used on Ebay, an install kit, and a rebuild kit (I'll be doing axle bearings too) for 200 total. Install time could be 2 hours from the time I crack the back cover to 6 if I have to re-shim the pinion a couple times. Just a thought.
Women prefer good handling to quick rides!