Either one, both are known to work. I'd just get the T-400.
Hehehe, I auditioned Eterna V2 already. I owned Eterna V1 so my opinion will be slightly biased.
The biggest difference between the V1 and V2 is the bass. The V2 have a lot more bass than the V1. If you switch between the two on the same song, you'll feel the V1 isn't that bassy heh.
V2 also have slightly better treble than the V1. Rides, Hi Hats, cymbals and snare sounded slightly better on V2.
For me vocal sounded about the same. But the bass in V2 overpower the vocal a bit.
Just my 2 cents.
Do you mean the V1 has more bass than the V2? To my ears the V2 is certainly less bassy than the V1. There is a slight reduction in sub-bass, but the main change seems to be the reduction of the mid-bass hump that made the V1 sound a bit bloated at times.
I think the change is for the better. With the old Eterna, you pretty much had to be a basshead to like it. The new version takes it out of the niche a bit, making it something that a non-basshead would be more likely to like than the V1. It's still a bassy IEM and the general sound signature/balance of the old one is still present, it's just not so blatantly bassy anymore.
My V2 isn't yet fully burned in but I can't possibly see it taking a full swing and becoming more bassy than the V1. Please do share your thoughts. Was the V2 you auditioned burned in?