Of course Nana Hotel can not be beaten on location, but there are better hotels, i think. I even liked when i stayed there a few years ago, but it was clear that is was getting old. And that was quite a few years ago.
Regarding Ibis, i would agree with Lone Ranger. I also have their card, for staying in some Accor hotels in the past, in Europe and in Africa (i dont recall any asian stay) and Ibis, in fact, a good deal, if you dont want anything fancy.
Ibis location is not 100 out of 100, if you think about NEP, but 90 would be fair.
There is a small con for me: the lack of swimming pool, even if i could live without it, as from BKK i will go to Pattaya and i will have lots of time to enjoy pool.
But, this time, as i am afraid i will not have much of a chance to do it in Pattaya (another topic it would be), i plan to try taking more than one lb with me to my hotel, at least for one ocasion. And, for that, from what i have read, in the area of NEP, Majestic Suites can be better (others to,, but i mean in the same price range of Ibis).
If it was not that point, yes, i think i would chose Ibis.