I think you mean the Attributional Style Questionnaire and the Life Orientation Test - Revised. If I'm wrong, my apologies.

I would say to use both. The ASQ is a well-established instrument with which everyone is familiar. But it was designed more to identify pessimism, really, since it was involved in the revision of the learned helplessness theory of depression. The LOT-R is much newer (which is both good and bad). More obviously linked with "positive" psychology, but also very brief (just 6 scored items!) and may be viewed with more skepticism by some readers.

Anyway, as a general rule it's wise to include multiple outcome measures in clinical research. You put so much effort into providing interventions, after all, and it's so easy to add another measure - and you never really know in advance which one(s) will be sensitive to the effects of your intervention.

Dear Stephen (I hope you don't mind me calling you by your first name?)

Apologies for my late reply. I would like to thank you very much for your insightful reply which is very helpful!

Have a great new year

Ibrahim

You can also try some Optimism scales:

https://core.human.cornell.edu/resources/measures/optimism.cfm

http://web.stanford.edu/class/msande271/onlinetools/LearnedOpt.html

They are relatively new, and may not have been standardized, but worth a look anyway.