I use Excel. Apps generally seem to be focused on tracking spending, and are less useful for modeling future changes. If I want to look at my actual spending in more detail I can use the banks apps for that, the spreadsheet is more future focused.

I have been working on the spreadsheet for years with gradual improvements all the time, and it is exactly customised to my needs. So I can calculate my pay (which is variable and based on a ludicrously complicated structure), allocate the money based on a mix of set and percentage figures, model the impact of future changes such as increases in power costs or getting another pet, and estimate at any time how much I have accrued for utility bills not yet received.