Should I bring euros, dollars, or Turkish lira to Istanbul?

Euros and dollars are accepted almost everywhere in Istanbul, so there's no need to exchange in advance. The only caveat: avoid 500€ notes, as they can be refused or difficult to exchange.

A practical approach is to buy euros or dollars at home and exchange them for Turkish lira once you arrive in Istanbul. Exchange offices are widely available.

You can also fly with Turkish lira already in hand — they're accepted everywhere. But euros and dollars work directly in many places too, so either approach is fine.