Ok in that case. The goal is to use a cipher suite that works well on your device that is still secure. AES is accelerated on most processors these days. But you’ll want to confirm that by looking up your specific cpu (both host and client machines!) and checking for AES acceleration.
AES-128-GCM would be my suggestion.
UDP mode provides less overhead, so it should be faster for you.
Alternatively you could use IPsec instead of openvpn but that’s a chore to configure. But it has the benefit of being free and being natively supported by many devices.
You would still want to configure an appropriate cipher suite that’s fast and secure.