I don't know how CarPlay is, but Android Auto restricts the apps and app interactions you can do in the Android Auto user interface. On my phone the only apps that show up are google maps, spotify, and my podcast player and my phone interface I think.

You can control Carplay the most relevant parts with buttons. Next-previous track, volume, voice commands, probably more I can't think of.

Not to mention that yes, a bigger screen probably is better. Bigger target = easier to hit. The legality can become a lessened problem, depending on jurisdiction. Using your phone while driving is often specifically illegal, but using your car's infotainment system might not be automatically illegal (it might count as distracted driving or whatever, but the threshold of proof is higher).