Larry,
My recommendation to you is to purchase every cheap, used mouthpiece you can find with clean tip, rails and table. Experiment and see what fits you best. This will evolve over time, and a mouthpiece you once loved may not continue to fill your needs, as your tastes and capabilities change.
Assuming a relatively leak-free clarinet, no single change has a more profound impact on tone, clarity, and ultimately--confidence than one's MP. It is the most critical component. I do not have the metric capabilities to measure the floor and roof of mouthpieces, as I'd like, so I cannot provide anything scientific for evaluation.
I have some mouthpieces that are fabulous in the Chalumeau, and lousy in the Clarion, and vice versa. It gets a bit unnerving sometimes, as a reed change can have a drastic impact on how a mouthpiece played previously. My assumption is that you will not have one MP that does everything for you, and will need at least three. I have dozens and I go back and forth, making myself half-mad. I will say that the Vandoren B45 is a very solid all-rounder, but I never found it exceptional at anything in particular. But now, sometimes that is exactly what you need. I have a great, very hard to play G. Bundy (3 facing) which I find phenominal in the higher Clarion, and rather dull in the Chalumeau. It requires a tremendous amount of air, but it is remarkably crisp and consistent. My Selmer HS* is a very fluid MP with a very wide range for bending, but I find without a rock crushing embouchure, it locks the reed closed against the tip, blocking all airflow, and squaks in the low Clarion, when I am not carrrying a consistent, extremely forceful charge of air. It annoys me to no end.
My favorites currently are a LeBlanc 2C from about 1950, a Woodwind Co. Robert Marcellus #3, and an un-branded 1920s-1930s Chedeville.
One last thing: Reed placement is critical. When I fit a reed, I make sure it is as perfectly centered as I can eyeball, with just the ever-so-slightest bit of the tip visable (Quite literally just barely visible, so perhaps .002-.003" of an inch), and absolutely no more. Never allow your reed to hang past the tip.