Re: OP. There's no hard-and-fast answer, and I've learned not to take well-meaning offers of exit-row seats from check-in or gate people unless I know the real situation. Mebbe someday I'll do a flow chart of the decision process.

You do need sites like seatguru to be warned of hazards like protruding doors (a real irritant), lavs nearby, or immovable armrests. On a non-full flight I'd rather get an empty middle seat with a movable armrest, but sometimes the seatmaps can be deceptive, especially on LCCs. If the flight's full you might as well get the immovable.

Another factor: No kids in the exit row. A positive fer shur.

One of the better exit-row experiences I've had recently was getting the whole row to myself - even though the plane was over 90% full - on a VLC-JFK DL flight because only 4 or 5 of the passengers on the whole plane understood English well enough for the crew to be comfortable they could communicate.