The Dukoff is the most famous mouthpiece with a step-baffle inside: http://theowanne.com/knowledge/mouthpiece-features/baffle-shapes. They mainly sound very bright and are commonly played in situations where you need to "cut through" other loud instruments such as guitars, bass guitar and similar in rock type situations. There are other mouthpieces out there that have a step-baffle, such as the Vandoren Jumbo Java, Lebayle Studio, Saxscape Downtown or Rico Metallite, amongst many others. I have tried several step-baffle alto mouthpieces, all of which I find a bit too bright and slightly thin sounding, and finally settled for a Phil-Tone Meridian for pop/rock/funk playing.
Playing mouthpieces with a step baffle is usually harder and they are easier to play with a larger tip opening and a softer reed. I usually play alto mouthpieces with a 0.078" tip opening, but my favourite step baffle alto mouthpiece (Barkley Pop 8) is 0.102".
A Dukoff is not cheap at £144 or so, but Howarth do them on a trial period, as do Dawkes - http://www.dawkes.co.uk/accessories/dukoff+alto+sax+metal+mouthpiece+-amw480.html
It all depends on what sound you want to produce. What mouthpiece do you currently play, where are you based, and what music do you most want to play on sax?
ps. I note from elsewhere that you live in Herts and play a Selmer S80 C**
Kind regards
Tom