Both series feature dirty jokes and randomness (Nupu Nupu is probably more random). Nupu Nupu actually features similar plot to God Save the Sugekoma-kun! in later volumes (as one of many subplots). You see in God Save the Sugekoma-kun! we have a perverted student targeting his teacher, but in Let's Nupu Nupu it's the other way around. If you found either of those series funny, you're ought to read the other one too.
Both of those manga are veeeeeeeeeeeery random, though Helvetica Standard even more so than Let's Nupu Nupu. On the other hand Nupu Nupu is quite crude and also contains some dirty jokes. If randomness is what you seek, then you shouldn't be disappointed with either of those series as they deliver it in spades.
Both manga are a collection of short and extremely random stories. Both can make your head spin and utter some WTFs. Let's Nupu Nupu is suppose to be comedy and Nickelodeon won't necessarily make you laugh, but if randomness is what you seek, you know where to look.