If you had all the wheels off the car and had to put them back on the car in any order, which tyre is the most important?

the tyres that are best should be on the rear so not to cause oversteer. 

yes agreed, bold tyres on the back axle on frosty roads and in snow causes oversteer.

In the uk, going around round-a-bouts puts the most force on the nearside rear tyre that should be the best tyre.

 I have always understood that best should go on rear as the result of losing grip at back is more dangerous than losing grip at front, from the point of view of car spinning out of control

Depends what you mean by 'best'...

When the edges wear off the fronts (usually through over zealous cornering and roundabouts) I tend to stick them on the back, still with around 4mm tread in the centre and the same age as the fronts, but technically they're the 'worst' ones...

 

If best means highest grip I'd put them on the side which drives the wheels so for example with my car I'd put grippy tires on the front as it's front wheel drive. 

1 hour ago, zain611 said:

If best means highest grip I'd put them on the side which drives the wheels so for example with my car I'd put grippy tires on the front as it's front wheel drive. 

That's wrong best grip needed at the rear on a fwd car

1 hour ago, pragmatix said:

That's wrong best grip needed at the rear on a fwd car

Lol I need to do my research 😂. I'd thought as the front wheels move the car it's best to have grip there as the front wheels are receiving the power and having to steer

4 hours ago, iantt said:

the tyres that are best should be on the rear so not to cause oversteer. 

+1 absolutely