Yes, you are. These are two very different cities and you'd be crazy to let the (minimal) differences between aircraft dictate your choice.

First thing - time of year has a big impact on your visit to BA, less so in Singy. So if you are planning on going in the south american summer then BA may be a better idea.

Depending on the length of your trip you can easily get internal flights elsewhere in argentina from AEP. Patagonia, Mendoza and Salta are all great. If you opt for Sing the city isn't very interesting (cf. HK) but you can at least hit most of SE asia within a couple of hours.

Personally if you're flying in the next few months I'd defs do BA. If you haven't spent much time in SE asia then perhaps Sing but just don't expect much from the city itself.