I use RS Means, MS Excel and and personal past performance. RS Means is not bad product but it has its limitations. It is targeted fo general contractors and the like. For me anyways, their labor times and material costs are for the most part on the money, even for remote Alaska if you apply the correct mulipliers. The problem I have with it is some areas are lacking in the line items and others they go overboard. RS Means covers all aspect of construction so it is not as definitive as you would expect from a electrican specific software.
The beauty of RS Means is that the data is compiled from nationwide sampling. That is why I like to use it for the labor time. If for some reason a particuar task is taking longer then the national average, I know I have a problem that needs addressing. It is an excellent reference to see how your labor times add up to industry averages.
By combining both RS Means and Excel, I can get a good estimate. In the same workbook, everything is broken down automatically by catagory for cost tracking during the project so I can see what is working and what is not.
I prefer Excel over Access. In my mind it is simpler to use and more people have it on their computer then Access if you share data electronically. If you really know how to use Excel, you can customize it where works best for you. Excel is one powerful program for crunching numbers.