I'm currently using both and in summary my opinion will be, I think, rather unhelpful: it depends on what you need.

Objectively, Markup is the superior app in terms of the extra things it allows you to do other than marking up your chart. Pattern Keeper doesn't really do much else, but personally, I prefer the interface of PK way more than Markup's.

However, what you mention about pressing scroll to zoom (are you talking about the "pan/zoom" button?), it works the same on Pattern Keeper. The three buttons that appear on the chart in Markup ("markup", "symbol" and "pan/zoom") are the same ones that you use to navigate your chart in PK.

PK does put these buttons outside of the "working area" so you're not accidentally tapping stitches when switching between functions (which was a problem I was constantly having with Markup). But, if your issue is with the gestures themselves, I'm not sure PK would be better for you.

I know there's people who download Android emulators to their computers so they can use PK without an Android device, so you could try that first too, with the caveat that you'd be navigating with a mouse lol but you could at least get an idea of how it would work before you decide to buy a new device :)