Which ever one I am running.
Well, at first it was all Book 2, all the time. Made sense as that was all I had. Dabbled a smidge in MT and T4. And before I traded it to my friend in the Ranger's (1/75) I ran some Traveller: 2300 (yeah, I kick it old school like that).
Now, of course I use Traveller5 rules and I have am having the Void's own time of trying to get Range Bands (which I do so love from CT Personal Combat) to work on a hex map with miniatures. And by Gods above, I use miniatures!
*And a moment of silence for those fallen Grenadier Imperial Marines now MIA, presumed KIA, along with the ancient Map of the Near Earth Stars and the cool flywheel powered LASERs*
*Now a joyous celebration that my Space Fleet is five ships strong, Thank you, My Patron!*