If there were no Looney Tunes, I guarantee you there would be no SpongeBob.
Everything should be taken in with the knowledge of it's context, and Looney Tunes' humour was revolutionary at the time, there was nothing else like it, and it hasn't aged a bit, you watch it now, it's still freaking hilarious. The characters are great, the writing is great, the physical comedy, the animation, I could go on, it's gold.
SpongeBob is still great and everything, but it hasn't been as consistent. The episodes haven't been good in years and it's not exactly the most consistent show in the world. It's humour isn't as timeless, I can't imagine a whole lot of it working 60 years down the road. But then again, it may, we don't know. It's not exactly fair comparing SpongeBob to one of the most influential cartoons in the history of forever because we're yet to know how SpongeBob will be seen in that time.
then again, personally, when it comes down to it, Looney Tunes for moi. Classic.