Helmet mounted light is the easiest, though suffers from not giving you useful shadows to judge bumps etc. The problem with seat tube mounted is that your legs tend to get in the way - you’ll tend to get a lot of moving shadow from them which is pretty distracting.
I made a light mount to fit under the handle to move the light a lot further forwards to try and reduce that - it seems to work. Post Your Current Projects Here is my first version for use with my old home-made light - the second version was a bit of plastic pipe bolted on in the same place for use with a commercial lamp designed to bar mount. However that’s not on any more as I now have a brake and haven’t worked out a good way of fitting the light along with that, so I’m back to just a helmet mounted light.