Depends what's available at the time.
Grass lets you keep blowing on it for ages but its unreliable in wet
Birch bark is easy to light, good longevity, hot and useful in wet but not great for lighting with embers
seed heads are hot, easy to light but go out quickly and any humidity makes them useless
Pitchwood, is hot, long burning good in wet weather but require shaving which isn't always possible with cold hands
Feathersticks are most reliable tinder form but difficult to make with cold hands or nowhere except wet ground to make them on
Generally the easier a tinder will light in warm weather the more useless it is in wet or humid weather while the tinders that don't light quite as easy do better in cold weather.
Personally given the resources I use a combination of tinders for example, lighting seed heads which in turn lights grass which lights feathersticks which light birch bark.
But again just whatevers available is good enough