Bookkeeping core
QuickBooks
The ledger underneath the screens is the first thing I check, and I found no public information on double-entry, a chart of accounts, journals, opening balances, or a period close — the only captured material is a privacy statement. A bookkeeping core this unevidenced lands at the bottom of the scale.
Xero
The evidence evidences invoicing, bill entry and reconciliation, but not one word about a double-entry ledger, SKR03/SKR04, journals, opening balances or a period close — for German books that's the entire engine missing. I'd be buying an invoicing app with an invisible ledger underneath.