Yeah! I even argue with myself about it...
I'm not very happy with the little comparison I did a few posts back. The truth is, if you seat the phones different, you can get the exact opposite result. Compared to choosing tips and seating them, the difference between these phones is small. Having said that, I don't rettract anything in the comparison, because it all seems to be right, even if it's all secondary effect. This is why I only comment on a couple of small things, and skip the big picture stuff--it's just hard to compare them.
Whatever you do, get some different type of tips and in different sizes, try them all, and figure out for yourself which one(s) to use. And, by the way, you might decide to use different sizes in each ear.
I've heard that Westone designed the Shure e5, and looking at the two, you'd think they were different product models of essentially the same phone. They also sound as if they're different versions, if they're voiced differently. The Shure has the first few inches of wire stiffened to help hold the phones in place when you rig it right over your ear, but even with this, there's no clear advantage compared to the lightness of the Westone--the Shure method doesn't work well enough to outright beat the Westone. I'm at a loss to decide in comfort as well.
The best recommendation I can give is that if price matters, just go with the UM2. If price doesn't matter, well, maybe like me, you'll have a hard time choosing beetween them on sound quality or anything else. Good thing I have both and don't have to decide. Then again, I often prefer the Ety over either, but the difference here is obvious. Like I said, it's going to take a good while to sort this all out.
A bit more, although I'm not completely clear about this all... Some people say the Shures are more musical, and the Westone more faithful or flat (frequency response). I agree. The shures emphasize overtones (Maybe that's what people mean by more musical.) which, in my humble (no, make that confused) opinion, is part and parcel of their looser bass/slower decay. From the opposite side, this can make the Westones seem hard by comparison. (Or depending on how you choose to describe it, dull, flat, or lifeless.) I note this particularly in solo piano (Chopin) where the Shures seem to add echo/hall presence/space/however you prefer to describe it. It also comes through with drums, where the Westone gives more of the initial dull thud, or rather, less of the ringing note that follows. (I'd call this a dry sound.) Another way to put it is Shure is more musical, Westone has more PRAT. Finally, in the high end, the Shures seem to have less distortion, although I don't know what this is exactly.