I've always been in favor of longer spawn times, as they first of all make it more interesting to fight over control points, and second of all because it makes me hold onto my life. But as was said, it's mod-specific.
Forgotten Hope 2, for example, will have very short re-spawn times, precisely for realism purposes. In World War II, which it is based on, people died left and right, so implementing short respawn times would work best for that mod. Imagine playing Omaha and dying from an MG, then wait 30 seconds, then die again, then wait 30 sec, then die again, and so on. It wouldn't work. Far better to implement short respawn times. In Project Reality, on the other hand, the world favors long respawn times, as it's based on the modern battlefield.
When it comes to First Strike, the problem is that we have two very different factions - the Empire, which can afford to lose units and considers them expendable, World War I-style, and the Rebel Alliance, which needs to hold onto its forces. So preferably I'd want some sort of PR-style 'Insurgency mode' where the sides were not equal and the Imperials would have a shorter respawn time and more tickets, to simulate how the Empire has lots of expendable units. In contrast, the Rebels could have a longer spawn time and fewer tickets, but vehicles that last longer and some other advantages. But I have a funny feeling it'd be very hard to balance this in-game
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Edit: In FS, I'd like longer respawn times for space map to keep people from ditching fighters, and shorter for ground maps, to encourage firefights. Or just make it so that it takes some time for fighters to respawn. Probably a far better way of handling matters.
"One of the bitches actually gave birth while she was attacking, and her puppies joined in on the carnage."
--the awesomeness that is Boatmurdered.