I'm using 7D, pairing with 16-35 II... as my regular walk around lens
wonder shall I go for the 16-35 IS? worth?
also I haven't got my wide for APS-C , which should I go for?
I) New, 10-18 STM
II) Old, 10-22 USM
Guess I have to ask why? I feel like there are so many better options for a standard zoom lens on a APS-C. Why not the 17-55? Or something like a 24-70 or 24-105 if you want an EF lens.
If you're willing to spend that kind of cash on a lens then I wouldn't be lured in by the low price of the 10-18, unless it proves to be markedly sharper, which seems unlikely. So unless you want STM for video I'd stick with the tried and true 10-22.
+1. f/2.8 is going to be more important on the 7D, so for the required FOV the 17-55 f/2.8 IS is the better choice imho for a walkabout lens, than the 16-35 f/4 IS. 16-35 f/2.8 II is certainly doable -- its corner softness will be mitigated by the crop body, and it will serve as an upgrade path to FF, but it does not give you IS in the so-called "normal" FOV region (i.e. ~28-80 FF equivalent). Note also that the 7D's AF system will benefit from f/2.8.
But to help answer the question, you need to ask: in what situations does the 16-35 f/2.8 II fail for you? what capabilities does it lack that would allow you to take better photos? what are the situations where you have a low keeper rate? If the answer is "low keeper rate due to camera shake" then you need to add IS. If the answer is "low keeper rate due to motion blur" then for sure you don't want to give up f/2.8, while IS may not be important. you can see here that the combination of IS and f/2.8 may or may not be important to you.
I would also recommend you review the meta data of your 16-35 f/2.8 II photos and see what percentage of them use f/2.8. Consider too, that the region between 35mm and 55mm may be important to you as well.
I sold both my 17-55 and 10-22 but they were important regulars in my crop body bag. Only downside to the 17-55 is that it is flare-prone and needs a front filter. FYI I had a $250 repair experience gone way bad (on my 17-55 before it sold) -- took Canon four attempts and four months to get it right, so make sure you test your copy, and beware of purchases from individuals.