Sans would definitely be the more skilled of the two but all it takes is one hit to take him down. He can dodge fairly well though, so the fight probably isn't that one-sided.
In the story Flowey vs Sans happened many times and Sans WON EVERY SINGLE TIME. Flowey himself admit this in one of the neutral endings, and that Sans is what stopped him from reaching Asgore and the human souls, even with him resetting.
In the story Flowey vs Sans happened many times and Sans WON EVERY SINGLE TIME. Flowey himself admit this in one of the neutral endings, and that Sans is what stopped him from reaching Asgore and the human souls, even with him resetting.
Sans won every single time... against regular Flowey. This is Omega Flowey, with 6 human souls.
Normal Flowey is pretty weak. Although it doesn't state it outright, Flowey basically says he couldn't beat Asgore without Frisk weakening him first.
Also, why are we using spoilers when the image itself is a spoiler?
Because we don't want those who hadn't played it to rekt it.
Anyways.
Even before Omega Flowey, he can summon larger vines etc as seen in the last part of the true route/genocide. There good reasons why he is not showing this on Frisk/the player