Two very different places and I like them both for different reasons.

Beirut itself is a party town if you like swish restaurants and clubs, but as pointed out above, you can get out and explore, ski, etc. Very western, urban and fast-paced in outlook. Lots of evidence of recent history if you follow current affairs.

Oman (my favourite country ) runs at a much slower pace, and there are not 20 things to do before lunch ! The trick is to slow down and take your time. Much more 'arabic' and 'islamic' but by no means strict, and you can still enjoy a beer in the major hotels. Lovely, friendly people.

Are you just based in MCT, or will you have a car to get out and explore ? Try to get up into the mountains for awesome scenery and views. Search previous threads for other things to do.

Assuming you'll lose a day to travelling, I'd do 2-3days in Beirut and 4-5 days in Oman.

Enjoy !