I'd say it really depends on what you're optimizing for.
When I'm going for a high score, I want the fastest time (and lost games don't count for anything). So I guess a lot, especially in the first few seconds, looking for good spreads and free information.
When I'm in the mood for a logic puzzle, I go for the best completion rate (percentage of games won). Then I click a single corner and work with whatever I get, guessing again only if my remaining options are guesses anyway. (The corner eliminates at least one bad endgame).
When I just want a fun experience, I go for most games completed in a session. In that case, I click all four corners to start to eliminate bad endgames. Those aren't a fun experience.
When I'm going for a high score, I want the fastest time (and lost games don't count for anything). So I guess a lot, especially in the first few seconds, looking for good spreads and free information.
When I'm in the mood for a logic puzzle, I go for the best completion rate (percentage of games won). Then I click a single corner and work with whatever I get, guessing again only if my remaining options are guesses anyway. (The corner eliminates at least one bad endgame).
When I just want a fun experience, I go for most games completed in a session. In that case, I click all four corners to start to eliminate bad endgames. Those aren't a fun experience.