The difficulties with using plasma cannons over plasma streamers is that the cannon must fire a contained bolt of plasma, otherwise it would spread out and dissipate.
To overcome this difficulty, the plasma must be contained within an energy matrix, in order to assure a compact and accurate strike on target.
All plasma weapons require some matter component. This amount is usually very small, given that plasma is very non-compact and highly charged. Goa'uld plasma cannons use small amounts of liquid naquada as both power supply and the requisite matter for transformation into plasma. Given naquada's density, when it transfers from a liquid into a plasma it carries quite the impact punch and gives the weapon's fire their distinctive golden/orange coloration.
Other elements and temperatures will yield different colors to the plasma. In general, the brighter the glow, the more potent the weapon. Also, colors along the blue end of the spectrum are more powerful than towards the red end. Those races yielding blue plasma cannons are usually the more technologically advanced, though there are a number of other factors to consider.
The density of the plasma orb will determine the amount of raw destructive force, which can then be varied due to temperature and constituent elements. Very compact orbs will target less square meters of the target, bringing their damage on one small spot. Larger orbs will spread the energy out over a larger area.
The density per meter of plasma delivery denotes the strength of the weapon. Small personal weapons like the Jaffa staff weapon have about half the density of the Death Glider's weapons, though those also cover a much larger area of contact.
Plasma is positively charged because of electrons being stripped from the outer 'shell' of the atom. The number of electrons missing determines the potency of the plasma and how forcefully it will react when it contacts other atoms(target's molecules). An element with a high starting number of protons/electrons has the potential for greater Ion charge, but getting that element into that highly ionized state is not easy and requires great temperature, pressure, and other more complicated atomic manipulation.