While we're talking about ECDSA + Android compatibility, one should also note that there is one incompatibility that one might want to be aware of:
Android 7.0 has a bug, where the only supported elliptic curve is P-256, meaning that the P-384 curve used by Let's Encrypts E1/X2 certs cannot be handled by this Android version. The Android version advises ECC support though, so I presume that this scenario will simply break (handshakes usually fail with "illegal parameter" TLS alert from my tests). 7.1 is fixed though, this seems to only affect 7.0. Older than 7.0 (e.g 6.x and below) as well as 7.1 and newer works fine.
If you want strong Android compatibility, sending just RSA with the compatibility chain (the one Let's Encrypt will soon use by default) is the best way with Let's Encrypt certificates. Everything else will offer slightly less compatibility with Android, even if you would send a ECC chain up to DST Root CA X3.