I would suggest the following:

a) For your primary spending card, use a Chase or Amex card. These will accrue miles that can later be transferred to a variety of partners.

b) In addition, rotate through and get the bonuses on cards from all the other partners. A couple of USAir cards here, a couple of United cards there.

Keep in mind that many airlines require some activity to keep the account open. It's not that hard. For example, USAir requires one activity every 18 months, so you can do an exchange on points.com (terrible conversion ratios, but so what if you're converting 6 miles from another program to 1 USAir mile, just to keep it active). You just have to keep in mind to do it.

Given your time frame, and the fact that you don't sound like you plan to use many of the miles before retirement, you probably have time to cycle through the partners more than once.

Also do remember that the awards can be and are devaluted. As an example, Air Canada had some very favorable rules on international travel, but then started charging "fuel surcharges" on almost all their partners.

Personally I'd suggest the Amex Preferred Rewards Gold as your primary card. $175 fee (waived first year), 25K signup bonus (not that great), but 3x on airfare, 2x on gas/groceries, and 15K bonus when you spend $30K in a year. You might also get a Chase Freedom (which does not allow travel partner transfers) and use their rotating bonus categories, then later on get a Sapphire Preferred and now you can transfer the points to travel partners.