This MAY help some...
Mouthpiece characteristics.....
Here's some thoughts on mpc characteristics. It would be wise in making ANY choice to remember that your choice needs to be a moderate/comfortable one for yourself alone.
Inner Rim Diameter
A large diameter generally enables the lips to vibrate more freely. It will also aid in the production of a bigger tone but if too large, the tone will be too open (unfocussed). In some players a smaller diameter can sometimes lead the use of a spread embouchure to gain volume of sound which then in turn leads to excess mpc. pressure in an effort to close the lip aperture once more. Excess mpc. pressure leads to inefficient endurance.
Cup Depth
Basically, the deeper the cup or overall total cup volume will darken the tone. A more shallow cup will give a brighter tone. For playing in the upper register a mpc. that is more shallow than average will give the tone and support required to perform in this register.
Shallow cups (at the extreme end) will make the tone thin / edgy
Cup Volume
The mouthpiece(s) of your choice need to suit the style / sound of the genre you are playing in. Using multiple mpcs. for multiple styles must result in extra practice on each particular mpc relevant to that particlar style. This will help to cope with the types of articulation/dynamics that you will meet within those particular styles. The larger the cup volume the fuller and louder the tone; the smaller the cup volume the softer and thinner the tone. If you choose a cup volume at either end of the extremes, control will be compromised. If you find switching mpc's difficult you are probably too mpc dependant.
Inner Rim Bite or Alpha Angle
The sharper the bite, the more grip is perceived. With a flatter or rounder rim, less grip is felt but more comfort acquired. Personal mpc. pressure plays a big part in choosing a mpc which will aid performance.
Backbore
The backbore volume and shape can affect pitch greatly. The backbore has several tapers, an initial and an average taper. If the initial taper is greater than the average you have a backbore with more volume, less resistance, and different harmonics. The diameter of the backbore also influences timbre and resistance. The length of the bore affects the blow resistance too. A narrow backbore results in increased resistance, brighter tone, and easier playing in the high register. A larger backbore decreases resistance and gives a darker tone and easier playing in the lower range.
"U" / "V" Shaped Cups
Most U shaped cups have a fairly sharp shoulder which results in an easy to play resistance and a well defined bright sound. V shaped cups have a smoother, rounder shoulder which produces low resistance and softer, darker tone.
Throat Diameter
The throat is the narrowest part of the mpc. bore. The diameter and length of this set the restrictions for playing resistance (back pressure). A narrow, long throat gives a high level of resistance which then in turn equates to fast response/brilliant tone and an aid to playing in the high register. A wide, short throat is more playable in the lower register and results in greater volume of tone but requires a great deal of air support from the player.
Model Numbering System
Most companies have their own way of numbering their Mpc's with the differences in Rim / Cup / Throat Specifications. The Schilke 12A4a can be deciphered as this...
The "12" part of this mpc. is the inner cup diameter.
The "A" is the cup volume plus shape.
The "4" is the rim contour.
The "a" is the back bore.
Mouthpiece Weight
Light weight mpcs. produce fast, flexible response while heavier mpcs. produce a more focussed tonal core. Much the same can be said for horns too!
Mouthpiece Finish
Gold plating IMHO helps with lip flexibility and is more suited to the player who uses a wet embouchure but is not so suitable for the dry lipped player who requires more grip. Silver plating is generally preferred by dry lipped individuals. Gold plated mpc's also tend to keep a constant temperature better. Solid silver adds to the weight and therefore adheres to the above.
Rim Thickness
A thick rim provides greater lip contact resulting in extended endurance but lip movement is limited therefore in extreme cases you lose some flexibility. A thin rim gives flexibility and control but provides less support for the lip thereby causing fatigue earlier than a mpc. rim of more average dimensions.
On people using one mpc for all playing, I have only one comment.
The 'performnce criteria parameters' of that particular individual are probably not that disparate to warrant a change of mpc style in the first place.
WHICHEVER MPC. CHARACTERISTIC YOU CHOOSE TO EMPLOY AS A POSITIVE, MEANS YOU'LL HAVE TO DEAL WITH IT'S OPPOSITE NEGATIVE IN THE PRACTICE ROOM! 
