These things are rare as hell on Leviathan- there have been 10 sales in the last year in the Jeuno AH, and I just got one. Hubie is possibly the best smith on Leviathan server, made it on the first try!
Speaking from the Phoenix Server, the options for a decent great sword in the late 60s are strictly regulated by your budget. The prices range from about 40k for a Zweihander to 2.5mil for Balmung. I see many DRKs with in-betweens such as the currently 500k Mythril Heart.
Looking at damage ratios however, Zweihander +1 has a significant lead over the Mythril Heart (And Balmung as well, in terms of unmodified damage, but Balmung has other benefits), ~.0172 vs .0166. The Mythril Heart has Dispel, but that isn't very useful in an exp party, in my experience.
The Mythril Heart's only real advantage is TP generation. It has a high enough delay to hop to the next bracket of TP per hit, which gives it an advantage in TP per second. I'm not sure of the exact numbers (the guide at Gamefaqs on weapon skills may be slightly off), but slower great swords will generate more TP.
The bottom line is that, since the Zweihander is shown up by swords with flashier effects later on, most people don't consider its dependability damage wise, and even its +1 version ends up being MUCH cheaper than anything else with similar stats. A Zweihander +1 runs about 150-250k on Phoenix. Compared to the meager benefits most other great swords offer in the 60s for a much higher price, I'd say it's definitely worth it, whether or not you're just hitting 60, or have used a normal zwei for a while and are balking at the prices of fancier great swords.
nah, don't need to think that you don't have a life by knowing a correction of the name. it's cool though, at least here a zweihander is a very damaging weapon :D.