I've flown Etihad twice now (BRU-MUC-AUH-BKK-AUH-BRU and BRU-AUH-BKK-AUH- BRU) and I'm a very satisfied customer, to the point that I'd pay a premium to fly them over most other airlines (also because they're the only airline flying from BRU that have their hub about midway ; we have few direct flights to asia).
They allowed me to take my rather heavy (folded) bike as part of my luggage, no questions asked. I was very happy with their inflight service (had a small snafu on the necessery overnight stopover in AUH though).

Standard seat setup in economy is 2-4-2 on both A340 and A330 (3-3-3 on B777). On my last flight with them I was upgraded to a 2-3-2 configured cabin - that A330 seemed to have a 4 class layout. I didn't know they had premium economy seats. Problem in giving more seat advice is that they have quite a diverse fleet in my experience - also I'm personally not a big fan of bulkhead or exit seats.

I booked on their own website, and preselected my seats when booking (they changed my seating every time though - I guess they wanted my seat to keep groups together - I was travelling alone ; ended up in better seats every time). I usually select aisle seats on the inside row somewhere in the rear - I always hope to get a free seat next to me - I'm quite big so it gets a bit cramped otherwise.