a dedicated E6B calc, but those may be banned
Certainly banned for any written test for PPL, CPL, ATPL & IR exams, but for any PPL nav flight you can plan any way you like. It's really down to the instructor to nurture the correct way to plan flights.
I would always start by teaching the fundamentals of the triangle of velocities. Depending on someone's knowledge of maths, this can simply be mentioning it and them nodding, or having to actually go through trigonometry. Once they realise where the figures are coming from I would go through the manual flight computer, since this shows the triangle of velocities reduced down to something useful and manageable and reinforces the fundamental point.
Once they have completed the Nav exam, possibly after the QXC I would then encourage the use of electronic planning tools, since this is more what they will use in real life. However, they still need the fundamental understanding from the onset of where these figures are coming from and how to do a rough calculation in their head.
With any computer it's rubbish in, rubbish out so be careful when you're planning that you don't end up with a useless plog through a silly typo.