Yuu☆Yuu☆Hakusho, JoJo no Kimyou na Bouken Part 4: Diamond wa Kudakenai Recommendations
Both manga involve Japanese teenagers gaining supernatural powers. Some characters in both series are quite similar to each other (Yusuke & Josuke, Kuwabara & Okuyasu, etc.). They can also get quite dark and grim by Shonen Jump standards, although "Diamond" has a lot more bizarre/wacky moments. Both were also written in the '90s.
Both mangas involve 90's teens who have supernatural powers. (The duo of Yusuke and Kuwabara in YYH is very alike to the Josuke and Okuyasu one). Both mangas involve very original powers mixed with hilarious humour, battles and slice of life style. Although Diamond is Unbreakable is more Slice of Life and Yu Yu Hakusho is more battle shonen, they're very alike and if you liked one of them you surely like the other.
Both works are set in the 90's (within Japan).
Both star cool and enjoyable delinquents as their series protagonists.
Both protagonists start of as pretty spooky and intimidating to others around them in their own ways, but they learn to appreciate the many different things that they come across within their new experiences and growth throughout the course of their respective stories.
Both protagonists also have a former enemy/rival who then later become their best friends, as well as becoming an awesome duo that share many comedic moments and badass characterization together (The protagonist's best friend in these two works may very well be their series' best character).