MSA,
First point, don't ever choose an aircraft type based on routes and overnights. They depend very much on the whims of the route planning people, and are very likely to change while you are on that type.
As far as routes go, the 320 does a lot of short intra-Gulf flying. It also goes to BOM, CCU, COK, KHI, LHE and some others on the subcontinent. It goes to CAI and KRT in Africa. It does the north-western Middle East (BEY, DAM & AMM) and IST, LCA and ATH. The only overnights however, are in AUH and occaisionally in DXB.
The 767 does the sub-continent, BKK and now to Birmingham. But as I said, this could all change tomorrow.
Salary is the same for any type at GF, but because the 320 does so many short sectors, it is hard to make overtime (>75hrs/month). I know the 330/340 guys are making O/T every month. I don't know about the 767.
Personally, I would go for the A320. Much higher level of technology, and readily transferable to 330/340.
The 767 is becoming a bit of a dinasoar. (Others may not share this view!!)
Also, the F/Os on the 320 are moving to the 330/340 in less than two years at the moment.
As for basing, push for BAH. (The only base for the 320 & 330/340)
Hope this helps.
Good luck.