Giving the poor reputation of Antoine d'Orléans in Spain, due to his duel with Henri of Borbon, but as well his strong political stances and constant shenanigans, Alfonso would be the better alternative overall. Even Republic would have been seen as a better alternative.
You had no real foreign support for Antoine either, not even in France (whom main concern was to avoid an Hohenzollern's candidacy) due to inner political stance and a general distate for Antoine considered as possibly abiding by pro-Prussian stances.
https://www.persee.fr/doc/rhmc_0048-8003_1969_num_16_3_3036
Basically, Antoine's candidacy wasn't really viable to begin with, and apart from every candidate being unavailable and Republic somehow not being an option on the table...