As others have mentioned, the first step is to figure out what you want, and then figure out which cards offer the best benefits. Some questions to consider are:

1) Which airlines do you use and how easy is it to get either reward flights or to upgrade with points? Do they charge high redemption fees (like BA's ridiculous fees)?

2) Would free hotel nights be a better value? If so, which brands do you typically stay at for business and for holidays? I tend to focus on Hilton and Marriott because they have a wider range of hotels in the places I travel, and at prices where I'm willing to pay $ as well as redeem miles. Plus, one of my company's preferred chains is Ritz-Carlton (affiliated with Marriott).

3) Will you benefit (at work or for personally) from achieving elite status through the use of credit cards? For example, Continental is my company's preferred carrier and I fly about 10 times per year. I also live near the EWR hub. So it's worth it to me to have the Chase Pres Plus Mastercard. Although it's expensive, I get a Pres Club (now United Club) lounge membership, free bags when I travel and I earn flex elite miles with $ spent. My husband and I also use the Hilton Amex because $20,000 spend gets us Gold status, and that translates into decent upgrade rates, free breakfast, free internet etc.

4) Don't forget the extra point-earning opportunities from using a reliable internet portal. I've found Marriott's to be the best. I make most of my internet purchases by clicking through Marriott's portal. As a result I usually get between 2 and 6 points per $ spent, plus the points I get for using whichever card I use. You might be able to take advantage of this for some of your corporate purchases - e.g., Staples, Dell and other computer retailers etc.