Always expect problems during the high season.

I've been on such rubbish planes that airworthiness is my number 1 priority.

The first 3 are similar although 1 & 2 offer more comfortable long-haul service. Qatar Airways are really stretched now and suffering from delayed flights. Etihad needs better seats in the forward cabins.
Gulf Air is struggling. I was once waiting to board one of their flights and heard them paging the CREW requesting that they head "immediately to the aircraft". I kid you not.
5 is no frills, best value for money, my parents flew it from Kuwait to Doha and said it was alright.
No idea about 6 but I imagine they should have the best tea.

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