Many people I know in the tango scene would not know how salsa boils inside of me. There is a reason for this: I know the salsa repertoire as a musician. I know all the percussion parts, the bass and piano. I can hear these musical elements -- they are not just a blur of sound as they once were. Much of the music has a history of friends and magical moments (just as tango has now). And still today, I see salsa as having certain advantages for those loved salsa first or learn it after learning tango first.
The Mood Advantage over tango: Salsa is mostly an upbeat, happy music, and in the right venue, people can be upbeat and friendly. Tango can have deeply meaningful lyrics, but there is tendency of melancholy even when the music gives no clue through the major key or happy melodic line underlying it.
The one-song-one-dance Advantage: Tandas (dance sets usually fours songs) are great in tango, but in some respects I love having just one song at a time. The one-song-one-dance rule makes it possible to escape a torture dance or just continue dancing if you both agree. Also, women who are not dancing for a whole tanda are sitting (often unwillingly) for 15 minutes.
The fast feet training Advantage: Anyone who is a good salsero will also have an advantage when dancing the milonga (a faster more rhythmic type of tango, which one will hear for about 7-10% of all songs played at a traditional tango party -- 3 or 4 out of 40 songs).
The cultural Advantage: What? Yes, salsa also has it's cultural advantages: Dressing well is the rule at a true salsa bar. In Europe and America (the only non-Latin scenes I personally know), tangueros are nearly always dressed two to three levels down from the women. Not true of a good salsa scene. Tangueros would never dress 3 levels down from the woman on a dinner date! In the best salsa bars in the US and Latin America, men wearing jeans wouldn't be allowed to come in the front door. If they slipped in the back, I doubt that a woman would allow him to dance with her.
The Ubiquitous Advantage of Salsa over Tango: Salsa is everywhere. On Fridays in my middle sized town in German, it is 10 minutes away rather I usually must drive far to dance tango. The same is true in the US. Because of the distance and price of gas ($9 a gallon), driving far has forced me to get back my salsa feet. Now, because of tango, my salsa has alternative steps that we do as a result of the music. Dancing with someone that knows tango allows us to improvise to the music very much like tango.
The tango advantage:
Tango has so much to offer salseros because of the concept of the woman waiting. My role is to be the musical note or impulse; her role is to be the just-as-important musical rest. Music cannot be music without the distinct roles of note and the rest.
Tango is an amazing dance that has transformed my salsa because tango has taught me to follow the music and how to portray what I am next planning to do with my partner. Tango has made me a much better salsa dancer than before, just as salsa helped me with the more rhythmic with the milonga's upbeat tempo.
The combination of salsa and tango.
You will find many who were once salseros/salseras who now dance exclusively tango. That is not true the other way around. Tango, once learned well, offers everything salsa has much more. I taught a young woman in a small US military community in Germany how to dance salsa. Innesa learned lightning fast. Soon I introduced her to tango, and upon returning to salsa and bachata, she was making stops and slow-motion moves in salsa/bachata with me. Someone asked me, "Are you professional dancers?" Dancing musically looks professional and choreographed, but it is just normal in tango. Later, when she did a tango demonstration with me at a dance school in front of teachers, they asked us, "Who did the choreography for that!?" Even trained dancers saw the professional look and exactitude of musical steps as professional." If tango can do that with any dance, then it truly is the dance of all dances. Sure, salsa may have its advantages, but nothing can replace the power of tango to transform salsa or any other dance to be more musical and fun.