I'm used to zero shown as last player for most games (as it's the most common) now, but I don't like the idea of zero.
First of all, part of the issue is the wording of the "players left". The OP used "players in reserve", and if those words were used, of course I'd expect zero to shown on last player, as "reserved" means "not in use". But if I was on my last player, I'd say, "I have one player left," which leans toward showing one. I'll call zero shown as "players reserved", and one left as "total players left".
Some games need to show total players left; the one OTTOMH is atari 2600 kaboom!, where the "players left" was actually part of what caught the bombs. And don't remember which ones, but I prefer games that offset or bracket the current player apart from the "players in reserve". Something like the following:
^ ^ [^] <--- the current used one braketed and in color
Again, don't remember which one, but a tag team fighter game shows both players, the one in use in color, the one not used greyed out, and if "dead" were grey and 'X'ed out.
The reserved type has the same issues with me. If it's a reserved type, it has to start with three in the queue and none active in the screen, and one the queue has to disaper at the same time the one on the screen appears, preferably in a synced fade in & fade out visual cue (and repeats each time you die), or something like that so I know those shown are in reserve and not total left. I think part of it is that reserved type shows only two, so it feels like I start with two players (I'm used to three players).
Basically, I can live either as long as it's explicit in which one it is. If it's not explicit, I don't like like them.