They're complete different books.
Harrington on Hold 'em is dedicated solely to NLHE tournament strategy. It's very in depth on the topic and it's a very good text if tight-aggressive tournament poker advice is what you're after.
Note that it doesn't cover cash games though, and if you're talking about 1/2 and 2/5 then you probably want something that does. Harrington has another book, Harrington on Cash Games, which I haven't actually read but I've heard good things about.
Ace on the River is simply not a poker strategy book. It's a fascinating book to read, and I highly recommend it if you want to become a more well-rounded poker player or if you're seriously considering taking up poker as a full time occupation.
But there's not much specific strategy content in it. It addresses a bunch of other topics like managing your money, philosophy, psychology and (believe it or not) there's even a chapter called "Poker and your Sexuality". When it does address strategy, it's from a very big-picture viewpoint.
Cliffnotes: Harrington on Hold 'em will tell you how many big blinds to raise with 87o at a given stage of a tournament. Ace on the River won't.