Alcance or Alcanza
 

In the sentence below, I chose to write "alcance" (subjunctive), and now I question whether I should have written "alcanza" (indicative).

El primero en llegar hasta la cima será el ganador, y el que menos altura alcance será el perdedor.

Please tell me which is the better choice, subjunctive or indicative, and why.

I would use the subjunctive here, since you're talking about an event happening in the future.

If you meant, "The first to reach the top will be the winner, and the one attaining the least height will be the loser," that could be translated as «El primero en llegar a la cima será el ganador, y el que alcance la altura más baja será el perdedor». You may also use what you wrote, but I would rephrase it: «alcance menos altura».

You may also opt to use the present tense, merely defining the parameters, and use the indicative mood.

Thank you, Rusty.