the view when long haul flying as a SO used to be nice. India, Europe, China, polar ice caps etc. The job itself is s*$t boring. Not sure on the pay aspect, expect to be away a lot more....however when you get to the 737, you'll be on a similar lifestyle to a Dash. And good money.
Id go for mainline over the middle east. The LWOP guys have the distinct advantage that they know when (if the choose) they can leave. Not to say they aren't having a great time though!
Id jump on the mainline list ASAP, wait it out and go to the 737.