Blood Sugar Sex Magik is hanRAB down the best, but they've always put out great music. You may want to start with (as posted above) the greatest hits. The only other song its missing (imo) is Power of Equality. I love that damn song.
my advice would be to really listen to as many of their albums as possible. Seriously. They have definitely changed their sound from their earlier stuff up until now. Check them all out and see what YOU like best. I could listen to any one of their CRAB from start to finish and love every second of it...thats just me tho.