power checks-into wind
 

whats second best? direct tailwind, or wind across the blades, that one seems to give a bit of vibration.

Don't think there is a second best.
I was always taught that the reason for into wind is engine cooling.
Aircraft engines are designed to operate with ~a hundred knots of airflow blowing by. That's why they are set to run abnormally rich on the ground and during initial climb.

Any extended ground running entails a risk of overheating and/or spark plug fouling. If the wind is light, probably makes very little difference.

When they were done CofA flight checks with wind across the blades to see max rpm.

I believe power checks are best done into wind, to maximise cooling, and this was critical on engines like the merlin. Unfortunately some pilots think you can only do power checks into wind, so if your doing power checks, a little consideration for other aircraft that are likely taxi behind you is good and incline the aircraft forty five degrees either side of the wind. I can't really see that there would ever be a need to do power checks with the wind behind you, unless it's a very light wind.

it was just a thought, the PA28 seems quite heavy to turn in a confined area to get it round into wind and then back again, just concerned about scrubbing the tyres unnecessarily .

I have found that a light tailwind is better than a light headwind for cooling. The prop has more 'bite' on a tailwind. I am talking about a normal run-up.

For piston engines make every effort to run up into wind. That applies to war bird liquid cooled RR Merlins as well as Cessna or Warriors. The engines are usually tightly cowled and there are baffles to direct prop wash and cooling air over all cylinders. That includes rear cylinders and the back parts of the engine where there are ancillaries.
It is all very well to be the nice guy and please others by turning at 45 degrees from into wind so they are not affected by prop slipstream during your run up, but in the end it is your responsibility to undertake a safe flight - and that starts on the ground with good run up practices.
If another aircraft chooses to get that close behind you as to be directly affected by your prop slipstream during run up, then that is his problem - not yours. Having said that, good airmanship dictates you should check all clear behind you before you do the run-up.