AM Gardens is my go-to but, as noted above, you can just go for nearest to your gate. Food & drink wise they are similar but the layout and views of each differ.

2.5hr, you will have time to do both if everything is on time and you are mobile. There is a train to speed things up.

There is priority security at the transit security and at your gate (there is gate security for flights to the US).

Signage in the airport is good, and you can supplement this with the "HIA Qatar" app on your phone.