Check The Wizard of Odds (see link)
Following the basic strategy above the house edge in Spanish 21 is 0.76%. However if the dealer stands on a soft 17 the house edge is only 0.40%! This is lower than the Atlantic City blackjack game at 0.43%.
Usually the dealer will hit a soft 17 however some casinos offer the more favorable game in which the dealer stands on all 17's. Locations that I know of or have heard of where the dealer stands on a soft 17 are:
All casinos in Atlantic City
All casinos in Indiana (only verified at Trump Hotel and Casino)
All casinos in Ontario, Canada
Foxwoods, Connecticut
So I'm assuming that you'd be playing in one of the above locations.
The strategy charts on that site are easily to copy/paste so if you have a colour printer you can make your own little charts.
(Seems every post I make about rules comes from The Wizard of Odds! You can be sure his charts are accurate, and better than Scoblete's or other popular writers. Thank you Mike!)