both will do the same thing.. tunes are the same on both, adjustable parameters are the same on both... custom tuning would be the same for both...
I sell both the inTune and Trinity programmers, and I also offer a package deal as well that includes my custom tuning at a discount so you'd save some $$.
You can find info about them, as well as links to my Package Deals, Testimonials, purchasing/ordering, etc. on my site here: http://www.diablewtune.com/package_deals.html
as for the difference between the two... I actually have both the inTune and Trinity for my car... tune wise, the tunes are the same. adjustable parameters are the same, and of course my custom tune would be the same as well...
The Trinity has a few more features, including a performance monitor for 0-60, 1/8 mile and 1/4 mile times, etc... bigger color touch screen... graphic virtual gauges for monitoring data... it has a windshield mount (like a gps)... you can watch/view the data without having to hold it, since it's mounted to the windshield...
The inTune is smaller (it's the size of a credit card), it does not have the performance monitor, and does not have the graphic virtual gauges, etc, but it's less expensive...and it's a little easier to use than the Trinity when it comes to data logging and importing/export tune files for custom tuning, since you don't have to use any extra software - everything is just copy/paste with the inTune.
So really, it's up to you which one you'd want... if you don't want/need the extra features/bell-n-whistles, then you can go with the inTune - and it's less expensive...
here are links to their user manuals so you can check them both out to see which one you'd want:
Trinity user manual: http://diablosport.com/manualFiles/Trinity/Trinity_Comp_User_Manual.pdf
inTune user manual: http://diablosport.com/manualFiles/inTune_Comp_User_Manual.pdf