IMO, there is currently no stable 4G device/system due to immaturity of the network and the fact that 4G radios suck power at 3X the rate of 3G.
Even just using the devices as 3G can be problematic, depending on what towers and upgrade level the network is. Not to mention if you live in a fringe area for 4G, you might have steady data connection grief.
TB: IMO, it seems that the weakest option of the current 4G devices is the TB, since a power sucking mess in 4G and problematic with 3G/4G.
Charge: If you MUST have a very good camera and highly value a display, the Charge has an edge, but the device is slow and the build seems weak and not solid by any stretch. There are also reports the reception is weak. The touch response of the display seems weak and has been picked up in a few reviews. Battery life appears best of the three 4G devices, but this a relative point, since all are hard on a battery.
Revolution: Same 4G battery issues as the others and has the weakest call quality of the three, but has some strong points. HDMI out, very good video support, 12GB of internal storage (it is also used for data, like the DX2) and appears to have the best radio reception of the the three devices (3G and 4G).
DX2: No 4G (perhaps a good thing for now?), sporadic MP3/Music issues (clicks & pops) and apparent heat spikes due mainly to some Flash content. As far as the MP3 issues, if I am not multi-tasking (setting changes or surfing) the clicks and pops happen about once during one out of five-ish songs (not THAT bad). If multitasking, at least once in every song (very bad). Another issue is random resets that appear to mainly be triggered by some Flash content and some video files using the stock player (does not happen using Rockplayer).
The good stuff in comparison to the 4G devices:
Much better battery life
Better call quality
Better radio reception (the Revolution appears to be good too).
Faster device for more demanding content and if you play game emulators like N64 & PSX.
The display has the best clarity and second overall to the Charge
Tons of add-ons due to the DX1
Better build
HDMI mirroring like the Revolution, but up to 1080p, rather than 720p.
In spite of the sporadic clicks & pops on the DX2, the Tegra 2 is better for sound quality.
As far as folks that are buying 4G devices now, just to "lock in" 4G, there is no apparent contract difference between 3G and 4G (both are same unlimited web package). The system settings profile for an LTE device may list "LTE", but the contract does not.
For somebody that does not want to wait for the Bionic or other next REAL wave of devices (all probably some form of dual core), the DX2 is IMO, the best device from a "total cost" perspective. Catch being the problems noted above and if they are fixed.
If we could take the storage space and video support from the Revolution- Display from the Charge- Power/efficiency, call quality, reception and audio quality from the DX2, we would have a near "perfect device".