I like the idea SLW has of investing their profits into miners whos situation SLWs management has intimate knowledge about. The investments in these small operations should payoff as multibaggers for SLW. IMO
As a silver streamer, SLW doesn't carry the same downside risk of mining failure. Also, it is tax free in the Bahamas. On the other hand, HL would be subject to Obama's proposal of a 5% mining royalty tax.
Owning SLW is similar to investing part of your money in a junior silver mining fund. Silver Wheaton finds the juniors with the best prospects, then provides them with capital to expand their operations in return for a juicy streaming contract in the $4/oz range.
I like both companies, but if I had to choose one, it would be SLW.