When we released Certify The Web v6.0 we defaulted to ECC keys but discovered later that versions of windows (server) upgraded from older versions often didn't have the right config enabled and would break themselves trying to use the new keys.
Broadly though, it's still just little bit early to tell on compatibility as I'm not sure absolutely everyone previously on an EC leaf is now on the full EC chain. We have seen some reports of compatibility issues here and there e.g. Mac RDP not able to connect to E5 wildcard - #35 by webprofusion
Hard (for me) to tell how the experience would fair with other CAs, I don't really follow their chain of trust story as closely, mostly because they have little or no community and don't talk to us 