Depends on a couple conditions to me...
I have both tanks by the way and they are my main tanks. When ever we go out for a day outing I bring both the AeroTank mega and my Nautilus.
Here's what I've found with them...
1. If you live in a high temperature area and are out in that high temperature a lot of the day then the Nautilus performs better. For me, my AeroTank mega when exposed to higher than normally A/C room temps tends to gurgle really bad and leak down into the air chamber where as my Nautilus can go out in the sunshine with me when it's 110° to 121°f outside and doesn't break a sweat. It's similar to leaving the tanks in a car with the windows up even if it's only for 10 or 15 minutes, I know when I get back to the car that I'll be using the Nautilus as it's not going to be flooded and gurgle it's head off.
However, beyond that I feel that both provide the same flavor but the AeroTank mega (again... for me) provides more vapor cloud than does my Nautilus, of course your mileage may vary since it will also depend on the liquid your using and what it's PG/VG ratio is.
I've tried the new Aspire BVC coils and to be totally honest, I think the difference is nearly undetectable (if it's detectable at all, I can't tell the difference) as far as flavor and vapor production goes. I did not notice any increased flavor between the BDC and the BVC coils in my nautilus. I've read a lot of others however that would swear that the flavor is a lot more intense with the newer BVC coils but I've also read and or watched a lot of videos from people saying that they either don't detect any difference or some that simply say things like "there's nothing earth shattering different between the two coils". Again, YMMV.
If I lived in a normal climate area then I'd probably stick with a line up made exclusively of the AeroTank mega's and one Nautilus with the stainless steel cage wrapped tank just to look at something different once in a while. Don't get me wrong, to me... These two tanks are some of the best mainstream commercial tanks available today.