If you can't wait until you beat the pillars again to get both of them, I say go for the Solar Eruption first.
The Solar Eruption has a wide arc of attack and it does so very quickly, making it very easy to hit a lot of enemies at once and with little skill or focus required. On the other hand, the Daybreak can onyl attack one enemy at a time and you need to have great aim to be able to use it semi-effectively at all. Plus, the Solar Eruption can attack through blocks, which is generally just convenient; said mechanic is, though, a very reasonable method to tackle the Moon Lord on expert mode.
The Solar Eruption is the weapon to go for all situations, really. Daybreak is great, but only in very specific cases.