Santana and The Police are coming to my city.?

Which concert should I go to? Or are both worth seeing?

If you can afford it - see both.
That said - The Police Box set "Message in a Bottle" is truly magnificent - a must if you're a fan. When it says "The Complete Recordings" - they mean it. If you must have "The Synchronicity Concert" - accompany said set with a DVD purchase.
Santana? There are a ton of hit compilations out there - they are all worthwhile. But - I would definately spring for the first 3 albums - no matter what. They are superlative! From there, anything goes - Carlos Santana never runs out of surprises! Oh - one more thing - look carefully, and find the Santana live DVD which was recorded in Mexico City - it's nothing less than sublime, and the sound quality is truly state of the art! Enjoy it for life, my friend!

be sure you go to Santana.

If I were in your place, I would go see the Police, however, if I could afford to see both, I wouldn't miss the opportunity to see Santana either.

Neither....unless your over 50!