Depends a lot on the amount you wanna to buy.

Small amount->LN

Big amount->on-chain

LN

It's ok to send amounts as tiny as 1sat via lightning, the bigger the amount the worse LN works, at least in my experience.

I've never had a problem sending 1, 21, 420, 210k, 1m sats, sending a couple of million though I often had to try a few times til it worked.

But that's expected, on every hop there needs to be enough channel liquidity to route the payment through.

on-chain

It's ok to pay a $5 fee for a $5000 on-chain tx, 0.1% is not that bad,

but if you just want to send/receive $5, that would be a 100% fee you probably don't want to pay.

It also depends on what you wanna do with it, like, do you wanna use it to zap nostriches, or buy/pay for stuff?

Or does it go straight to cold storage for the next decade?