I've read both authors, used both strategies, and would highly recommend reading all of Dan Harrington's books as well as all of Arnold Snyder's books.
Snyder may put down Harrington too much for my comfort, but Harrington has lifetime tournament winnings of $6,319,179 and Snyder has ???????? Can't find him on any list.
That said, Snyder's greatest value has to do with card room tournaments that are too fast for skill to be of any value and Harrington doesn't even go there. I think anyone who has read any of Harrington's and/or Snyder's books, can get great value out of both, and they should be re-read as you advance in your playing skill and continue learning more about poker.
Doyle Brunson's Super System 1 & 2, is still the place to start. Dan Harrington's Zone Poker is more of a conservative approach while Arnold Snyder's Rochambeau style with the Speed and Aggression Factors are more aggressive. I think both should be used at the same time, kind of like switching gears. I've even used the Kill Phil approach in some games. I like to blend all of these into the Art of War Poker, as a playing style.
I Never Bluff