Several things are important to look for. A good drywall company will have experienced people who have years of experience with the type of drywall work you need done. While it's not overly difficult to slap some drywall up, it IS difficult to make it strong and have it look good without wasting material. That's where experience comes in. Little things like which way you lay the sheetrock can make a big difference later on. A good company should also use only quality materials so they stand up to normal everyday wear and tear without being prematurely damaged and needing to be repaired. Drywall finishing and painting are more art than science and when done well everything looks seamless like it was always there. When done wrong, they will always be an eyesore and will reduce your property value. The most important quality as also the hardest one to see up front: attitude. They must value what you want and be willing to do the job right, even if it takes more time or material. It doens't matter how much or how little you paid for the job if it isn't done right or doesn't look the way you want. Getting the right company to do the job the first time means saving money on hiring another company to fix it later.