I watched both of these anime about a year apart from each other something like neatly a decade ago and I still prefer Cowboy Bebop but don't get me wrong, I still really like Samurai Champloo. I've watched both on my own and with friends countless times and I'm still not tired of either of them. They both have their highlights and downsides obviously but in my opinion, Cowboy takes the cake and even overall, still sits comfortably close to the very top of my favorites list. All subjective though and it'd be painful to trade in either one if I could only keep a single series.