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).

I've used both and Blockada is better mainly because it has a couple of killer features. One example is that it will keep the app alive, so that the power saving features of your phone does not kick in and turn it off.

Any experience with NetGuard? It has similar functionality and walks you through preventing the battery optimization from killing it.

I haven't really tried. Blockada never gave me a reason to.

How does this affect battery life though?

I have between 1-2% battery usage.

You forgot to say what timeframe.

No matter what time frame 1-2% is 1-2%.

The time very much matters. 1-2% per hour is much different than 1-2% per day or per week or whatever.

I assume that's Android's stats about what % of battery each app uses. If so, time doesn't add anything.