I did the post-grad BSW at Lakehead, worked as a Social Worker for a few years, and have been accepted to two advanced standing MSW programs this year. Given that it's the same amount of school either way, I'ld recommend going that route. I've also really appreciated the chance to take on placements and a professional role before going for my MSW as my interests now are completely different to what they were before I started. However, I had very little relevant experience before doing my BSW, so you might be a couple of steps ahead of where I was then. I don't think you can go wrong either way, really.