My first slot was a Bally EM... I like it but EM's are a challenge for me. My next was a IGT S plus which I LOVE. I have a few now. I then bought a IGT S2000 and loved it. I have more now! Then I got a Bally 6000 - wait I bought two! I had a blast learning something different and got both up and running, got the correct software to match the glass and reel strips.
I don't know what's better to have first but if you want a Bally 6000 spin and win, get one! There's plenty of help here if you need it.
I'm sure someone will chime in soon with pros and cons as well.