United is one of my favorite programs because of their one-way awards, great award availability, flexible routing rules, and wide range of partners and destinations. They have won recent awards for having the most available award seats, and importantly, these awards are easily searchable online, including almost all of their partner airlines!
One-ways permitted? Yes!
Partner flight redemption: MileagePlus miles are redeemable on all Star Alliance partners, including US Airways, Air Canada, Lufthansa, AviancaTaca, All Nippon Airways, etc., as well as some non-alliance airline partners. You can see these partners on United’s online award flight search results.
Off-peak and special deals: If they exist, I don’t know about them. Feel free to educate me in the comments section.
Award chart: Fair and reasonable; nothing ridiculously inflated but also no bargains.
Routing rules: One-way awards don’t allow stopovers. Open-jaws are allowed by definition because you can just put together two one-way awards for a creative double open-jaw. Now for the good stuff: United has incredibly generous routing awards on round-trip international awards from the US. They allow one stopover and two open jaws! This means you can: 1) Stop en route for however long you please at one point; 2) Depart from and return to different US/Canada/Hawaii cities; and 3) Arrive at one international airport and return back to the US from a different airport in the same region on United’s award chart. This leaves flexibility for super creative routings, and therefore AMAZING value for the amount of miles you spend.