Well, I don't own a laptop, so a Tweecer or EEC Tuner was not even a consideration for me. The Tweecer datalogs, and the PMS will also, but only with the optional software (and a laptop). All changes are made right on the PMS handheld unit, which doubles as a real time monitor, when not making changes. You can literally make a change at a traffic light with the PMS...doubtful that can happen on a "laptop tuner". The Tweecer has ability to change more parameters, but the PMS allows plenty enough changes to be made to dial in most any kind of combo. The Tweecer allows you to change electric fan on & off temperatures, the PMS doesn't. The PMS allows you to have three completely different tunes stored in it's memory, not sure on the Tweecer. Both do their jobs well...Tweecer, from what I've heard and read...PMS from what I know and have experienced. The Tweecer is slightly cheaper, but if you need to buy a laptop, that goes to more expensive. I believe that the Tweecer can be programmed on a home PC, but that would require hauling your pcm and whatever else in and out of the car, into your house, which hardly seems to be anyway to try and tune a car IMO. I can literally take off from a stop, know it's not quite right, pull over, make a one minute change, and try it again...as many times as necessary, with no headaches or trouble whatsoever. The PMS has settings that are changed in either percentages (fuel), or degrees (for timing). The PMS also has programmable menus for both nitrous and/or supercharging/turbocharging, which I don't believe is a feature on the Tweecers or EEC Tuners.
Ultimately, the choice is yours. Diehard Tweecer fans will say the Tweecer is superior...And diehard PMS users will say the opposite...fact is, both do what they are supposed to do, but IMO the PMS is much more user friendly, and easier to understand.
I suggest you read through the USER MANUAL and features (linked below), as well as checking out
www.stangtuning.com which also has a forum for Tweecers IIRC...
http://www.andersonfordmotorsport.com/pms/pms-50.html