The reason I personally dislike dollar coins (& I doubt I'm alone in this) is that they for some reason made them to be nearly indistinguishable from quarters unless you really look closely at them. Under most conditions of normal use it's very easy to accidentally pull out a dollar coin instead of a quarter without noticing, and the other person in the transaction may not notice either. I've occasionally been on both sides of that mistake. This was an obvious problem with the Susan B Anthony dollar and a main reason for its failure. I've never understood why they then proceeded to announce a major redesign to correct it, then issue the Sacagawea coin with nearly exactly the same fault. It's not like there's no other size, shape, or weight available for a circulating coin.

(Yes, I know all the bills are the same size, but we're used to that and the numbers are big. And the $10 bill is pink now.)