I've learnt so many versions of the Two-Step, What should I be using as my basic step, and what ballroom dance closely resembles the two-step so that I can use moves from it?

By Two Step, I assume you mean a Country Two-Step, as opposed to a Nightclub 2 Step (which is also danced in the Country and Western World). There are many social variations of Country Two Step (Texas Two Step, etc), but here is a basic descripton of a Two Step you would dance in a more formal environment , like in the UCWDC dance circuit:

1) Step forward onto the left foot for 1 count of music (QUICK).
2) Step forward onto the right foot for 1 count of music (QUICK).
3) Step forward onto the left foot and hold (2 counts of music, SLOW).
4) Step forward onto the right foot and hold (2 counts of music, SLOW).

- In terms of Ballroom dances, Foxtrot is the closest to Two Step, however they have two completely styles. Moves from one don't translate very well into the other. Foxtrot is a slower, smoother flowing dance. Two Step is a faster rhythm type dance with LOTS of fast turns.
Hope this helps!

I hate sounding antagonistic on my first posting, but I feel I should correct a couple things. There is no such thing as "Country Waltz." When we compete in UCWDC, we compete American Style waltz to Country music. Also, while the timing of twostep is similar to fox trot, it is not a smooth dance in the tradition of Fox Trot. It has a definitive rhythm and uses a lot of the same partnership principles found in hustle or West Coast Swing. You can find such syllabus patterns as telespins and pivots in two-step, and swing styled patterns like whips and baskets, or hustle patterns like egg beaters and illusion turns.

There use to be "Country Waltz" in the competition - been there. But so much of the country styling is getting lost, and looking like ballroom... it is a shame. Even the two step, hand placement on shoulder is being moved to the back, more ballroom. And good old swings are now WCS instead of 4 count and pony which was really exciting and fun to watch and do. Nothing against WCS but it really isn't country. The two step can be danced Slow, Slow, Quick Quick which I preferr because the Man doesn't tend to bounce so much when first learning to dance. He comes out of the gate a little slower and smoother that way. Delighted

I agree. The placement of the hand from the shoulder to the back automatically makes it a foxtrot and not a true Country Western Two-Step.