You definitely want to go with an architectural shingle. GAF timberline HD is the big seller at the moment. Certainteed Landmark also is big and is heavier weight per square than GAF. 3 estimates should be fine. Don't go for for any longwinded high pressure sales pitches. It is what it is when it comes to a roof. Have the companies tell you how much your roof measures so you can figure out what they are charging per square. If you're pitch is very steep the cost for labor will go up. Also if you have 2 layers on the roof now labor will be more.If any of the wood is rotted don't let them charge you anymore than 60 per sheet. in most cases that can't tell about rotted wood until they start tearing off. If you have any water leaking in now you probably will need new wood in certain areas. Some companies will try to talk you into replacing all the wood, not necessary unless over 2/3rds is rotted out.
Very important to make sure they install drip edge. A lot of companies don't in order to cut corners and save cost. You also want to make sure they install Ice and Water shield. Make sure they include ridge vent as well. Don't get talked into new gutters and downspouts unless your are in bad shape.
Stormpc gave good advice on fair pricing. 300 a square is too low so the company and or labor could be sketchy. 400 a square is fair and reasonable. Even 500 a square is ok as long as the labor and product is very good. Sometimes the guy who gives the estimate does the work himself so his profit is his labor and he will come in at 300 a square roughly. Often you don't know what you're going to get with this type of labor. On the other side there will be a lot of big named companies that will take a shot and try to go for 600-1000 per square. Thats outrageous and they're not giving you anything different than the other companies are despite what they say in their sales pitch.
One last bit of advice. Make sure you check on any company that comes out to your house. The only true way to do this is to call the Home Improvement Commission and give them the companies license number. If they have any registered complaints eliminate them immediately. You can also call the BBB but it"s the MHIC that regulates the industry. The Home Improvement Commission is set up to protect the customer, The BBB really is not. Sorry to be longwinded but choosing the right company is often very difficult because they all are going to sound great especially if the salesman is experienced. A bad roof install can become a nightmare you'll have to live with and often once the job is done it can be very difficult to get these guys back to do repairs and services. Ive been in the business for over 20 years and my father for over 50 years so we've seen it all. Good luck and if you need anymore info. please feel free to message me.