Honestly I can't see trying to say which is better when one ran 6 seasons and one is just about to start it's second. Dave Filoni was one of the main creators of "The Clone Wars" and is currently doing "Rebels". While I will say that "The Clone Wars" was an amazing show that bridged a lot of stories, filled gaps, and gave character to the cookie cutter clones we see in the movies "Rebels" will do it's share. To be honest "Rebels" is just the continuation of the Star Wars animated story line. If you have watched the trailer for season 2 you know some of the characters that will be showing up in that season. I know a lot about what to expect in season 2 of "Rebels" and I can't wait. There are little things that will be in season 2 that only diehard "The Clone Wars" fans will get. Bottom line is that Disney has done an amazing job between movies, animated, novelization, and comic formats to make a canon story line with as few issues as possible. These 2 series are just parts of a greater puzzle. You really can't say one of these are better than the other without watching and reading all the current canon material. Because there are things in the other formats that tell more about these series than you would know just watching them.
"A New Dawn"
"Tarkin"
"Dark Disciple"
Read all 3 and you'll find that there is a lot that ties both series into what is basically 1 animated series with a movie that fell between them.
So far I have read A New Dawn. I need to get to it.
I haven't watched rebels yet (hoping to soon), but I do love the clone wars, and own the entire series on blu-ray.
From what I've seen of rebels, I don't think I will like it quite as much for a few reasons
1) Cheaper animation budget (clone wars actually lost money I believe, but that's how lucas rolled, he wanted quality over profits)
2) Less epic, as at least in season one it's mostly all on one planet I hear, and you're always focusing on the core group who's basically together I believe.
3) A bit more "kiddie" from what I hear as well, although clone wars could certainly be at times too.
I hear ya on point number 2 but it helps when you realize they aren't coordinated and are trying to do their best without sticking their heads too far into oncoming enemy fire. There's a lot they can do against the Empire on that planet, so why not start there.