Once you have hired an architect (instead of a design/build firm), you will likely spend a considerable amount of time hammering out your plans. I recommend researching contractors throughout this time and gathering names of contractors that you hear about. We received several contractor recommendations in the course of finding an architect.
There are good and bad ways to find a contractor. You may find someone good either way, but your chances are much better if you choose a the traditional route of referrals. You may have noticed a theme here that I work mostly off referrals. Frankly, why wouldn't you use trustworthy referrals if they are available to you? Here are some good sources for referrals: 1) Friends, family, and neighbors in your area (preferably in your city/county); 2) neighborhood listservs; 3) Consumer Checkbook or Angies List; 4) subcontractors who you have used before (plumbers, electricians, HVAC, etc.); 5) your architect; 6) your realtor; and 7) yard signs (but ask the owners before you dive in).
In the case of the last category of yard signs, this is the least likely to yield the best results because in some cases the project is in full swing and the homeowner won't fire the contractor because of the delay that may follow. I asked a neighbor who I didn't know about construction being done on their house and whether they were happy and they vehemently told me "NO" and gave a list of about 15 reasons. I scratched that construction company from my list! You may get some good referrals this way, but I would take the other routes first.
In our case, I once again used my local moms' club listserv and recommendation list to gather a list of 15 or so builders. I checked and double-checked referrals and finally came up with a shorter list of contractors that we wanted to call and meet with.
There are several types of GCs. Some GCs prefer to work with particular architects and some will work with anyone the homeowner chooses (the latter is more common). There are GCs that are part of larger companies that handle multiple jobs at once and there are one-person shops where the GC is on-site every day and managing your project directly.
Although some people gain a lot of comfort from GCs that have their names on signs all over town, that also means that they are doing a lot of projects at once so you are going to be dealing with a project manager (who you may not choose) who runs your project and not the owner. We preferred to go with a smaller company where the owner manages the projects and gives you all the attention. I think you also get a better price from these types of operations because you are not paying for several levels of hierarchy, office staff, etc. You also can be sure that your money is going to your project and not another project that the builder is behind on.
More on interviewing GCs next time...
