Blackscale wasn't too bad, and most of the artifacts are pretty easy to snag. Don't be afraid to pledge Tarhyl, the gear is very replaceable with new content and as a rogue, your gear isn't really all that important anyway. There is very little in ToT that's a must-have for a rogue (though there are a few nice pieces that you will later replace). That's all WAY down the road though. If you plan on raiding seriously, I would wait to pledge a diety until you join a solid guild and decide you like it.
The most important part of pledging to a diety is that you want to have your core group of homies lined up first so you don't miss out on a big chunk of gaming with them. While it's entirely possible to just play a different toon to help the guild progress through your deity's raid zone then catch up at the next tier or whatever with YOUR toon, that's a path best left untrod.
Enthann used to be the primo rogue diety b/c you could easily max your chaotic points and still raid his zone, and the aug gave you a little worn attack leeway on itemization. (Was also nice having the enthann gate neck on my scummy alt to beat all the other scummy alts to the free raid spot killing orcs in cauldron, but that's a whole nother story)
Tarhyl used to be the ABSOLUTELY NOT rogue deity b/c you would miss out on Stoneculler (I still hate you torick) and Flarewynd and ToT used to house some end-game items and deep First Ruins is a choice xp/farming area. Now all of those items are very replaceable with the exception of the clicky on Flarewynd, which isn't a huge deal regardless, and there are plenty of other xp zones that are just as good as bloodfires in ToT. (I could be wrong on this but I believe you can still do the Eternal Well if you are pledged to Tarhyl, if someone could confirm/deny, then if someone else could kindly make it a moot point at the tip of Tarutao's content-skipping-spear)
The big criteria I'd look at (in no particular order) are 1) How bad will I miss raiding that zone, 2) How helpful is the aug, 3) How helpful is the gate neck, and 4) How likely am I to max my deity spec bonus
tl;dr: If you plan on raiding, join and decide you're stayin in an established guild before you pledge, if you don't plan on raiding, pledge anyone but Tarhansar b/c he's gay as aids
