I've used both but recently there was a discussion on Github about Blokada secretly reporting analytics to the developer. Given that the app is primarily used by the privacy conscious, it seemed like a bad idea. They just added an opt-out yesterday, but it was enough to go back to DNS66. The Blokada dev has been posting surveys to get feedback on various monetisation ideas recently (an anonymising VPN, merchandise, a pro version with extra features, etc) so I doubt it'll remain free, as in its current state, for long. I know everyone is entitled to try and make some money from their work, but I always worry about security/privacy apps when the key motivator is money and not helping the community stay safe. Compare pi-hole.
So I switched back to DNS66. Which is great, but you might need to disable async-dns in chrome://flags depending on your device. On Android 8 (Oreo) tablet, Chrome ignores the device network interface DNS preference and sends DNS requests out the physical interface, and not via the local (filtering) tunnel. My Android 9 (Pie) phone doesn't have this problem. Blokada worked fine on both but DNS66 only worked on the tablet when I turned off async-dns (which I think is a terrible, network-breaking feature anyway).