I have Neverfull MM in Azur and Ebene and many other LV's, but my NF's are my most used bags, they are amazing! Eva is also nice and I use her often, but you can't compare these bags. I vote for Neverfull, simply gorgeous and a classic LV.
I have both NF & Eva. I got them almost about the same time ( August & October of last year) I use the eva way more often than the NF. I think since I got the NF (mm Ikat), It's been out of the dustbag like 3x. So my vote goes for you know what... the eva clutch.
They are such different bags.....I have both and Palermo as well.
Honestly, I thought I'd use Eva much more than I do. I've taken her out to a few parties and events, but that is it. I use my Neverfull MM more for travel and general schlepping about books, papers, etc.
I have both the neverfull mm and eva and I love them both! I would be inclined to say you should buy whichever one you think you will use the most first. It's really about lifestyle. I use my neverfull as my school bag so during the school year I'm using it at least 3-4 days a week. Now that it's the summer I've downsized to my smaller bags because I don't have as much to lug around. However I should note that I have the old style of the neverfull and the new ones come with a little pochette that is removable so it's like you're getting two bags in one...