Smartbit is back after a few days of downtime (weird but ok). BlockCypher appears to behave well. An online instance of Blockstream Esplora is also nice.
Blockchair looks promising, but haven't tested it yet. For now I'll stick to the listed ones and switch between them in case of problems. If that approach fails, I'll go for deploying full node and communicating through json-rpc (or for node + own instance of esplora, idk yet)
Thanks for all advices.