I don't mind them, but I will say my preferred #Japanese vols per English omni is 2. Any more and it starts to become a bit uncomfortable. I'm willing to accept 2.5 at times too (I'd rather have 5 vols put into 2omnis than 3 vols). I think the most I have on one book right now is 4 (Yen Press's Another release), although I kind of want the Death Note vol (because it's kind of hilarious). I've seen the DN one in the store, I can't imagine the paper used is very thick/good.
I also prefer them when it's the first time they're being released (for example, a lot of Seven Seas titles). If you're curious as to why they do that in the first place, Japanese rules want $$ based on number of books printed, not number of books sold like US rules. Making 1 book instead of 2 means the US publisher has to shell out less money because they published one book, not two. And if it seems to be a title that they publisher thinks will sell less, it can be safer financially. Obviously this is hardly going to be a factor for something that sells as much as One Piece or Attack on Titan.
I'll say that for the Viz cheap 3-in-1 editions, I believe that Skip Beat is the only series that I collect in that format. But now that they all match nicely and stuff, I'd rather wait for the 3-in-1s than get the singles (even if I'm now 3 vols behind). Also, they changed the spine's font to match the actual series, I much prefer it over how their early Shojo Beat titles were all that stupid weird red font thing. I think it was done to "match" the Japanese release, approximately, but I guess the US consumers prefer the uniqueness of a proper title design. Still, whichever way I go, I kind of want them all to look the same, dammit! The worst thing had to be when Dark Horse changed where their logo went (top then bottom), then decided to back track, making all the spines look an unholy mess. As much as I complain about the old Shojo Beat font, I do give Viz props for continuing their long runners with that font, just for the sake of uniformity (I wanna say it's just Skip Beat and Kaze Hikaru at this point though)
Still, I say if you don't like them and have the option/money to get the single volumes, go for whatever you prefer. In the case of One Piece, you could buy those manga boxed sets, those have about 23 vols in them each and they're all the regular single vols, you'll save some money that way too.
https://www.amazon.com/One-Piece-Box-Set-Baroque/dp/1421560747/ref=sr_1_1?ie=UTF8&qid=1514206880&sr=8-1&keywords=one+piece+manga+box |