I am not a huge fan of the sousaphone. If i was given the choice i would take a marching tuba or contra any day. Its not that the sousaphone is bad, just i think there is better.
Mine is the epitome of everything people hate about sousaphones: sixty years old, three leaky valves, a narrow bore that means anything above D in the staff takes effort not to overblow, slides that must be tuned with pliers no matter how much I clean and grease them, small parts that match neither the original nor each other, general uncooperativeness, etc. There is no tuba I would rather play with the Balkan band that aims for a disreputable vibe. The sound is different. I do not prefer it in all settings, but it has its place. My Miraphone 186 is a better choice for most venues, but there are things sousaphones do well.