BrewR is a great tool for putting together a recipe idea in no time. I use it a lot from my Xoom android pad, because of it's modern and simple UI design, it's so easy and quick to work with. It doesn't necessarily offer everything you need though. Beersmith and Promash are much more time consuming to work with, and both offers real clumsy UI design, but you win on comprehensiveness, calculation accuracy and detail. Beersmith also offers the recipe cloud which is a great plus.
The real challenge for all these tools is FG calculation. This is where BrewR really falls behind. It does not take into calculation your mash temperatures, grain/sugar or yeast types. Nor does it offer any means of configuring yeast attenuation, so you end up with a very rough estimate of FG. It seems to be calculating your FG with OG as the only reference factor. So consider something like a tripel, which when mashed low, brewed with table sugar additions and fermented with a proper high gravity, high attenuated Belgian yeast, will end up with high alcohol and low FG. With such a recipe, BrewR would completely over-estimate your FG and provide a completely wrong picture. However OG and IBU calculations are acceptable. I use BrewR a lot, but I have learnt to disregard the FG it gives me, and improved my own ability to "guesstimate" a more realistic FG, based on OG, mash schedule, ingredients and yeast/fermentation.
Beersmith and promash will give you a good FG estimate, but it comes with a cost. You need to enter a lot of data into an awkward, old fashion user interface, and it takes a lot more time to formulate recipes using these tools. Oh, and you also need a PC to work them.