I've owned 17s and 617s and I think that the triggers are about the same on these guns. Obviously, there are individual guns with nicer triggers and some whose triggers are not so nice. But, as a group, they all seem to have similar double action pulls.
Which is to say, in my opinion, slightly heavier than for Smith's centerfire revolvers. Not so heavy as to be unpleasant but still, just a tad more resistance. I spoke to someone from Smith about that once and he told me that they do that deliberately because rimfire ammo is notoriously inconsistent and they wanted to make sure they didn't get light strikes. I have a 617 with a very light trigger, the product, I think of someone's trigger job done before I bought the gun. The trigger was a delight and I got a light strike about one out of every 6 rounds. I just replaced the main spring with a heavier spring and I'm going to the range this afternoon to see if that resolved the problem.