I believe the "artistic" version is the one where you step on beat 2. This involves considering the slow step not as a duration (foot down, now take 2 beats), but as a time interval. You have two beats for the slow count, so stepping anywhere within those two beats would still be on the slow count. This is the more artistic version as Jonathan described it where you move through the first beat before placing your foot on the second beat. Since you're still stepping within the interval of beats 1-2, you're still on the slow count.
The "regular" version, if you want to call it that, would have you stepping on beat 1. This is what people are used to, the slow takes two beats, so you step on the first beat and carry it through the second beat. This is also how most dances work as Jonathan mentioned. I knew about using the artistic version in foxtrot because our teachers tried to get us to do that in the advanced classes, but hadn't been aware that it's used sometimes in tango, too. I'll have to look for that on tapes of competitions. 
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James Marshall
marshall@astro.umd.edu
http://www.astro.umd.edu/~marshall