The best Places to look in order based on probability and ease of detection IMO.

1) Mars (water, methane, and potential for deep methanogens, potential surface fossil beds)
2) Enceladus (liquid water likely and potential for evidence jetting into space)
3) Europa (huge ocean likely with potential for ocean vent type biosphere)
4) Titan (massive reservoir of organic chemicals, active chemical cycles, liquid organics, deep hydrosphere, chemical disequilibrium)
5) Ganymede (deep ocean, active geology)
6) Callisto (deep ocean)

Some people consider even gas giants, Venus, and IO as possibilities for very alien forms of life, but I'm doubtful that any place besides Titan has much potential for a radically different form of life.

I think the odds of detection drop hugely between 3 and 4 but Titan has the best possibility of having truly alien life based on chemisty different than Earth's. The others might use a different DNA code for water based life with a seperate origin, but Titan could use a different solvent and chemistry that would be explosive at liquid water temperatures. It could even have two forms of life. Truly alien at the surface and water based deep below the surface in a liquid water ammonia mixture. Even if it doesn't have life it may be of huge use in finding out how life evolved if it has preserved precurser chemicals in it's deep freeze.

I absolutely hate that we seem to be headed to exploring only one of the Jupiter or Saturn systems more deeply for life in my lifetime. Europa was ahead of Mars at the top of my list at one time but discoveries over the last few years make it seem much easier to find life on Mars or Enceladus. I think the odds of deep life are on a par between Mars and Titan, but Earthlike life on Titan will be too deep to detect with existing technology.

I think we will find further evidence for microbial life somewhere else in our solar system if we push our technology just a little and explore these possibilities to the fullest extent of that technology.

Regards,
Mark