First of all I don't do any remotely scientific test with my lenses. I do really like my 55-200, and I think it's slightly sharper than my 18-150, especially at the long end. That's my most used EF-M lens after my 32mm. It's also around half the price of the 18-150 and I think one of the best bargain for the EOS M system. On the other hand, the 18-150 is more than enough for my needs and its main selling point is its versatility. I would say I find it pretty great for the price between 18 and around 120mm, and slightly softer after that, especially when doing landscapes. If sharpness is what you really want in a EF-M native lens, the canon 32mm or sigma 56mm are the way to go, but they are of course much wider.
What is more important in my view is to think about what pictures you want to take and in what conditions. Will it be convenient to change lenses ? Would the 55-200 be different enough from your 55-250 ?
Keep in mind that these EF-M zooms are consumer-grade optics. There could be a lot of copy to copy variations so what I said here is just my humble opinion about my own lenses.