Mig basics 101:
110v vs 220v:
110v machines top out at 1/8" steel max. Thats usually using fluxcore wire on a machine rated at 140amps. These machines are really useful for sheet metal and body work, but lack the power to produce good welds in heavier steel when used by the average welder. These machines also lack the power to be very useful at all with alum due to the low max output. The upside is that they are very portable and can be run from most 110v outlets. They usually only reach their max rated power however if used on a dedicated 20 amp line, so on average they run at a reduced power level on the average outlet. One of the big issues with small migs is that you can make a nice looking bead on thicker material that lacks penetration and has no strength.
220v machines: The "low" end machines usually top out at 5/16" or 3/8" steel with fluxcore wire or gas mig (both CO2 and C25). Larger machines can weld in excess of 1/2". They can be turned down to run thinner material easily. Many of these machines are designed to run a spoolgun for alum, and machines 200amps and up will run 3/16" alum+ depending on max output. The down side is they require a 220v outlet, similar to a range or dryer so are not as portable. There are some 110v/220v machines like the Miller MM211 that can run on both.
Fluxcore vs gas mig:
Fluxcore wire is similar to continuous stick welding. You have a flux coating that shields the weld and must be removed. It is messy and smoky and is generally the choice for outdoor work. It will tolerate a bit more contaminants than gas mig. Penetration is usually deeper than gas mig and is why most small "migs" are FC only machines. Also most small 110v migs only reach their rated thickness using FC wire. FC wire on thin steel is quite difficult due to the deep penetrating qualities. FC wire generally runs DC- so the polarity might need to be switched with machines set up for gas mig.
Gas: There are several choices for mig gases. FC migs converted to gas will need to have the leads switched to DC+ to run correctly. Gas mig usually is best done indoors or on calm days when a breeze won't blow away your shielding gas.
C25, 75% Argon/25% CO2: The usual gas mix for most migs with steel. It's the mix usually listed in the manual. Gives cleaner welds with a bit less penetration. Good for auto body work on thin metal as well as thicker steel.
100% CO2: A cheaper alternative to C25. Gives a bit more penetration than C25 so will often be listed for thicker steel on smaller migs. More spatter than C25. The extra penetration can make it difficult with thinner steel. Note an adapter or different reg is usually required to run 100% CO2 as most mig regs come equipped to run C25 / 100% Argon.
100% Argon: Used to weld alum.
Other mixes are available for spray and Stainless applications.
Alum: While many small migs list that they can be used to weld alum, welding alum using the standard gun is usually very frustrating due to the soft wire bending and jamming in the machine/gun. Mig alum usually requires a spoolgun or in industrial migs a push/pull gun.
