But, actually, he chose a stag because it was large, powerful, and fast. It could survive a werewolf attack (assuming the worst case scenario happened). When the Marauders told Remus they were animagi.
"James can you just not" "No Remus, you three look great in this lighting" "We hate you prongs" "No you don't padfoot" "Prongs, is this necessary?" "Yes Wormtail, you three look great, now shut up and let me take the bloody picture!