It's medium. One time our escrow changed, and they messed up applying our payment, and it took us FOREVER to get it straightened out. They had even started with threatening phone calls and using the F word (foreclosure) and it was all over a $40 misapplied payment. It was horrible.
On the other hand, about a year ago they sent us a Fedex notice that we qualified to refinance for free: no fees, no points, nothing. They were just going to lower our rate by half a percent. We were super suspicious and went through the whole process looking for the catch but there never was one. We could've possibly refinanced through another company for a quarter of a percent less, but we would've had to pay the fees and apply and all that. It was super simple and lowered our payment by almost $100/mo.
Our mortgage was sold to them shortly after we bought our house and I've never had an issue with them. All but one credit card became a chase account around the same time. Since I suddenly had a bunch of accounts with them, I set up a checking account and have half my pay direct deposited into it. I use it to transfer the mortgage payment and pay off the credits card that we use for points monthly. I do everything online and I don't think I've ever stepped foot in a chase bank even though there are several near my house. They frequently offer deals like $100 credit to set up a checking acct.
We used to have a mortgage with them, and the only issue we had was when we would submit extra payments. Sometimes they would randomly apply it to "pay ahead" as in credit it against e next months payment, versus applying to principle. We always paid extra, and I had to call them several times to get the payment credited properly. Just keep an eye on that balance!
Ours is through Chase and no problems. They also did our streamline re-fi which lowered our payment by 25% and we even got money back at closing! The paperwork for the closing was a little frustrating (they couldn't give us the exact amounts until the day of closing), but it worked out just fine.