Back when I first started shopping for a computer ( late 80's ), everybody used to tell me that the Mac was "the" midi computer. I met a couple of people that were talking up the Atari but not many. I know that I passed it up at the time. A MacII with 020 and greyscale monitor was @$10,000 Canadian at the time. The Atari was <$1000 and an Amiga 2000 was @$2000. A PC(386/EGA) was about $3500. The choice seemed pretty clear to me.
As far as midi, the Amiga wasn't the first choice for a lot of people but it did have some software. I met a guy in Alberta that was using an Amiga 1000 to run his light show and all his keyboards/drum machines with SoundScape which is how I first knew of the Amiga. Anyway, I looked at the Atari and I wanted an all around computer that would be good at everything and the midi ports on the Atari weren't enough to convince me to buy one.
I suppose if low cost midi computer was my primary concern, the Atari might have been a better choice but at the time I was basically taking a break from the music biz. @5 years on the road was starting to get monotonous.
It hardly matters now though does it?
Thanks to CommodeDoor, the Ameoba is no longer... and for that matter.. either is the Atari.