The Delta Amex is the best of the airline specific cards since you get double points for a lot of things and they run double or triple point specials from time to time. I believe you can also use your skymiles points for seats on any of the different Skyteam partners.
Starwood will give you 25000 miles when you trade in 20000 points. There is a Starwood Amex to get this one going. As with most, if not all, of the Amex cards there will be double or triple points on some purchases and from time to time for all purchases. We rarely stay at Starwood properties so you won't get many points from that to trade into airline miles, but it's a good deal anyway. You will spend at least 15K for hotels a year and if you use it to pay for your cell phone, homephone, cable, satellite, groceries, and whatever else you normally buy, you will rack up a lot of points.
If you use the company card you will probably be putting on from 30 to 40K per year (40K point limit per year with a roundtrip at 25K). The company card is the only one you get the airline tickets paid on for those points (at least as much on airlines as you spend on hotels). You'll probably be able to get 3 roundtrips every 2 years with this one and if it gets stolen the company is taking care of the bill- not you.
I've heard that the United Chase Visas are good for getting the 20 to 25K miles free with for each one and they waive the fee the first year. They have a few different cards so you can get a personal and a business (your own sole propietorship or a real business if you have one) to get a load of points. Then after 6 months you cancel them and apply again after a while to get the points again. Chase may have figured this out recently, but it has worked for many before. Amex doesn't fall for this ever so don't cancel an Amex and then get the same one again and expect the freebees twice.
As JustInfo said the SouthWest double dip at Hiltons (at least half your nights at NetJets) will get you tickets fastest (50 nights for any other airline versus the 32 for SouthWest).
Another way to get your tickets faster is to put all of your Skyteam miles into one account so it builds faster and gets elite status faster (mileage bonus per mile elite status). Continental, Delta, and Northwest can all be put into one of the accounts as long as the tickets are either booked with the account number you want to use or as long as you switch it at the gate before the first leg of your flight. Continental has the best Silver level point bonus- 50% versus 25% for all the others at the first elite level. You can also put all your USAir and United miles into either account. I suggest putting all you USAir miles into United even if you live in a USAir hub since United points are easier to use.
While lots of free airline tickets are good, airlines are still typically cheaper than hotel rooms for a longer stay so a lot of guys try to maximize their hotel points more than the airline points. If you plan on airlining to see family and friends then go for airline points, if you plan on airlining for vacation destinations, you might want to do the best you can for hotel points.