Should I give my pothos a bigger support or let it trail?

Either option works. If you want it to climb, use a sturdy stake or trellis that sits securely in the pot, then loosely attach the stems. A support that wobbles around may not do much for a plant that’s already leaning.

If you like the trailing look, let the vines drape instead. You don’t need to make every pothos climb.

For the sparse one, you could take a few cuttings and put them back in the same pot once they’ve rooted. Make sure each cutting includes a node, since that’s where new roots can grow. It’s a straightforward way to make the pot look fuller without changing the whole setup.

Also check its light. A brighter spot with indirect light may help new growth come in less stretched out.

I’d choose based on the shape you want, not because a bending vine means something is wrong. Let it trail from a shelf or hanging pot, or guide it up a support. You can also trim a few long pieces and use the cuttings to fill in the sparse pot.