There isn't really a good answer to this, because it really comes down to personal preference.
Time Machine is a great program IMO, but it's not prefect. It does get everything backed up, but you have to use the program to restore as well, and I've had issues with this. Especially when the backup drive has issues. And it can be more difficult to go in and retrieve files manually as well. You're locked into the Time Machine system. However, it is extremely easy to set up and maintains itself for the most part.
Clones are less simple to setup and maintain, but you can retrieve files easily with Finder, not having to use some program. And if something goes wrong, recovering the backup is usually a simpler process.
You're probably fine with Time Machine by itself. For me, having an extra backup is always nice just in case, but that's me. Like I said, it's all about personal preference.