get both they will not fight it will be like having two dragon in one tank, but just watch out for ur pleco they might sometime suck on the bichir body but other then that u got a super cool tank
I agree get both but make sure you do your research on the two. Aros get big and you need to make sure you have enough room for them. Just do your homework!
thats easy man get both one live almost exclusively on the bottom and the other on the top to middle. they will get along famously! but if you had to choose one get an aro. they are undoubtedly the most interesting to watch of the two.