I can't comment on Beersmith, as I have never used it, but more people use it than anything else. Can't go wrong that direction. I have been using Brew Target. It is open source (free) and designed and built by one of the HBT members. Seems accurate enough (though I have little to compare it to). Keeps track of recipes, has a notes section for tasting or things you may have done differently on brewday. A massive data base which seems to include all the major maltsters. I.E. if your recipe calls for 8 lbs of pale 2 row, you can select from Breiss or Weyerman or Rahr pale 2 row. Not sure if there is really much difference, but the option is there. The yeast bank seems to represent all "models" of yeast from White Labs and Wyeast, though the dry yeast section is lacking a bit. Pretty nice program especially for free.
If you have a smartphone you can also get Brewzor Pro for free. I use it to design recipes when the mood strikes away from home. There are some serious discrepancies between the two, so I mostly use it as a notepad and general calculator. Plug it all in to Brew Target when I have a chance.
I will more than likely be checking out Beersmith soon and comparing differences. If it is much better I will make the switch and buy it. If it is comparable I will stay where I am.
One to avoid, IMO, is Qbrew. Its not really a bad program, for the most part. Just a very basic layout and not as user friendly interface.