By default, CFWebstore only allows you to set one shipper to display rates for. There is actually good reason for this. As a certified UPS 3rd party developer, I am restricted by their licensing which does not allow me to display UPS rates alongside another shipper's rates. Not sure if the other 2 shippers have this restriction (USPS does not I know, but FedEx does I think as well) but since the custom shipping methods as well are not really compatible with each other, there really was no option but to leave the store configured to only allow one type of shipping. So when you see other shopping carts that offer UPS shipping along with other rates, they are often doing that in violation of UPS policy!
When I was recoding the shipping functions for version 6 though, I decided to code it in such a way that if you did want to use more than one type of shipping at the same time, this is very easy to set up and do with a very minimal amount of coding. Be sure if you do this that you know if the licensing for your shippers allows it; if you do this in violation of any policies, you are responsible for the repercussions of that and may lose the right to access their API.
So let's say we want to use both USPS and a custom shipping table method. You can use a custom shipping method with any of the other shipping types, you just can't use more than ONE custom shipping method at a time. For instance, you can not offer both shipping by price and shipping by number of items. To accomplish this would require additional coding so that each has it's own shipping table of rates. So let's look at offering USPS and custom shipping rates together. First, select the type of shipping you want to appear second in your store and configure all of its settings. Set up all your methods, shipping table, etc. Now, go into your database and find the ShipSettings table. This is where the settings for your store shipping types are stored. Take the row that is in there and make a copy of it to a second row. Save your changes and return to the store admin in your browser. Select the type of shipping you want to appear first in your store and save the change. Once again, go to the bottom of the page and configure all the settings as desired.
That's it! The store is coded to handle all the rest and should now output both types of shipping that you have configured. You may have to tweak some code here and there to get precisely what you want, but this should take care of the bulk of the work for you. Please note that the shipping estimator will only work for the primary shipping method that you have, it is not able to be coded to work for multiple shipping types easily, so cannot be used with this modification currently.