Another easy question !
It depends on what makes sense to you. Many users (and some of my clients) like to see all debts listed in one place (ie unpaid bills or aged creditors report) and so leave the VAT liability as a bill.
Other users (and many accountants) recognise that, under general accounting principles, debts to HMRC are not "trade creditors", and so prefer to have them shown separately in the payable account.
To add to the debate, you have the same thing with creating director/employee expenses, ie they default to being bills owed to the person, but you can toggle them to accumulate in "John Doh - expenses" type accounts. Unfortunately though, if you use payroll this will always generate bills in favour of employees (net pay) and HMRC (PAYE), so no toggle.
So, on balance, the short answer, stay with bills and ignore the payable account.