Howarth's is just past baker street tube station and a couple of left turns. 31 Chiltern street I believe.
www.howarths.co.uk
Mouthpieces are a very personal thing, I'm not happy with my mouthpiece on my tenor, it's a very cheap unbranded one and is very 'gritty' and gives a really harsh reedy sound. I spend all my time struggling to smooth out the tone when playing my tenor. I'm going to invest in a new mouthpiece, but not until I've found the sax that suits me first.
On alto I use a variety of mouthpieces. The most common are an S80 C*, which has a circle shaped mold inside. A Link STM 6*, which is completely empty of any molding on the inside. A very old Windcraft one which gives me the darkest sound. It has a rectangular shaped bit inside, but the mouthpiece is considerably larger on the inside than the S80.
The Link gives me a darker sound than the S80 but still cuts through and can scream brilliantly. The S80 gives a very bright, crystal clear sound very well suited for classical playing. The Windcraft is the hardest to play but gives the darkest sound but responds the worst over the range. The S80 is the only one I can get the altissimo consistently.
I find that ebonite mouthpieces are a bit better than metal, though on tenor a metal mouthpiece can have a really good affect.
It's very individual and the same mouthpiece will be awful on a different saxophone and with a different player.
For myself I have a sneaking suspicion that an Ottolink Tone Edge will be best suited, or a Jody Jazz classic, I found them really nice to blow.