As far as SCT goes, the X4 is the pretty bare bones unit. Basic color display, no bells and whistles, but gets the job done.
The BDX is essentially the Bully Dog version of the X4, acquired by Derive when they purchased Bully Dog about 5 years ago and rebranded under the SCT letterhead. It offers the same features as the X4, but in a sleeker "nokia brick phone" size and also offers Cloud functionality, making it easier to interface by allowing your tuner to push tunes to the cloud, and allowing you to email datalogs to yourself through the cloud, limiting the amount of time you actually need a computer for tuning. It's only available for SHOs model year 2013 and newer.
The Livewire TS+ is more of a dedicated monitor, it has a touchscreen interface that is much more pleasant to look at, offers track apps and performance monitors, and has a more refined RTM display.
All SCT handhelds can hold between 10 and 20 custom tune files depending on which model you choose, so no issue there holding the original and alternative tunes.
The newest offering to hit the Ecoboost community is the HPTuners RTD. It's just a dongle, so there is no standalone interface and it requires a laptop or Windows based OS tablet to load tunes and datalog, but I've really been enjoying the change of pace utilizing HPTuners for tuning, and the software is much more stable than SCT, especially on 2010-2012 models.