It could be their best, but it could be the worst. I imagine for each person it will be different. I think to really know where it fits in people should give it a good six months or more of listening. When you have a long awaited album from a band you love there is a tendency to be really excited by having something new. Either that or you hate it.
I don't mean don't discuss it, or don't say you love it (or hate it, if that is how you feel), but rather six months or a year down the road post on this album again. I think it would be great if everyone who posts their "Is this U2's best album ever?" opinions (when it come out that is) would keep a copy of their own post. Then six months later all those people could post their current views on the album. It would be really interesting to see how, or even if, opinions changed.
I mention this because I had this type of situation fairly recently myself. I'm a huge fan of The Church, who released their most recent album a little less than 11 months ago. I got it right away, of course, and adored it right away. I didn't post on it until I'd had it a month, but I did discuss it with friends in chat. I loved it when I first got it, and I still love it now, but it is interesting to look back at what I wrote then and see how my feelings have changed (first post -- I loved it all; second post -- overall I still love it, but four of the 14 songs are good, but I could live without them).
It's also a lot of fun to see how it fits in with the band's other albums (14 without compilations) after several months (for me in my top four albums of their's, in case you are wondering).
Just a fun little exercise.