I have a 6s and it often freezes on the native system apps too. I don't think that any of the later models are going to be immune to this. I can attest that older apps are often the culprit to stability and battery issues when new major iOS revisions are deployed. However, a new bug i noticed today was after using the official Reddit app, the system did not fade to black/screensaver and was on all night and ran the battery down for me (noticed this at 6:30 am, it was still on the Front Page- phone died 20 minutes later). The Reddit app was just updated a few days ago after the iOS11 version came out.
Freezes on the 6s that I have encountered are mostly native app related:
Email: native email client- freezes when trying to open, swipe to delete, or moving between folders- it's not a waiting on the network freeze, the whole screen and home button is unresponsive. Occurrence 20-30%
Photos: I do not open the photos folder very often, but after 11.0.3, it now takes me 1-3 tries to get it to open. Same issue when trying to add a photo within text message. Occurrence 30%
Messages: tapping the icon to launch the text messages does not always respond. Other times when it does respond, it loads a white screen with grey circles on the left (the contact initials/image). This is occurring frequently, 30%
Logging on to the device: most of the time the finger print reader activates, but other times when inputting the number code, the system freezes after the last digit. So there is a 3-5 second black/grey screen before you move to the home screen. Not a deal killer but more of the same issue.
Note: iPhone 6s, 16Gb (6Gb free space), iOS 11.0.3
Device was purchased new, not a refurbish and has never had a replacement part
I backup and restore to factory defaults after each major iOS revision, which I've found is the only way to keep the device in good running shape. I backed up/restored after iOS11, but do not usually have to do this after each patch update.
Apple guys: Something's not right with this one guys, there's a lot of unresponsive UI issues here.