 If you liked
Trigun
|
 ...then you might like
JoJo no Kimyou na Bouken Part 7: Steel Ball Run
|
They both started out as shonen and then became seinen. Both are westerns with fantasy elements and have a lot of gunfights. Both stories present many philosophical themes and they both have an excelent cast of characters. Also they both have really good comedy.
If you enjoyed SBR I think you might enjoy Trigun a lot too. Although if it's the other way around, I would highly recommend reading or watching the previous parts of JoJo's.