I played BOF4 first and it was big mistake, as I couldn't go back to BOF3 after that.
Combat was just so slow and boring with much worse sprites and animations, I couldn't play it for very long. I got to the point where Ryu is an adults and nothing fucking changed by then, so I just dropped it.
Supposedly its story is better than that of BOF4, but combat is so much worse.
So probably play it first and 4 next so you won't fall in the same trap that I did.
That said I absolutely loved story and characters from BOF4. Most jrpgs have at least one or two annoying cunts in your party forced on you, but in there I absolutely loved everyone.