NOOOOOOOOOOOOOOOOOOOOOOOOOOOOO!
DO
NOT
GET
Unless you like crappy tone
MG Series cabs are designed to work with Marshall's entry level MG series amps, which are solid state. Totally different thing here. I'd suggest shopping used first of all. Older speakers generally sound better because they are broken in, and your tone will be much better.
Guitar cabs and speakers are really the last item in the signal chain, and they definitely have a very powerful tone shaping capability. I'm not sure what your needs are but depending on the style, your cab choice will fine tune your tone to be what exactly you need.
Here are some basic tips.
1) speaker affects tone. Consider how much power handling it has as well as the amount of breakup or 'cone wobble'. I find for more vintage, lighter, and classic tones speaker breakup is great. Any cab with Celestion G12M 25s or G12H 30s (or whatever copy you get) will get you in the ballpark. While both have great cone breakup and warmth, the G12H 30 is tighter with more defined highs while the G12M 25s are more round and midrangey. For a good middleground, go for a G12T 75 for a more cutting high end, phat lows, and scooped mids. Now, for the quintessential metal speakers, Celestion Vintage30s are upper mid heavy with very aggressive and defined highs. When driven hard, they ROAR. A Classic Lead 80 is more of an 80s sound with little to no breakup. Great for leads, as the name suggests.
Now, you can get whatever Eminence or WGS Celestion copy you want. Some people like Eminence, while I like what I have heard of WGS speakers so far. They KICK ***!!!
2) Cab affects tone. Each different cab colours how a speaker sounds. For instance, open backs tend to be more 3D and better for clean while close backs tend to be great for crunch and thump. I find that certain designs with vents or ports tend to retain characteristics of both open and close back cabs which can be nice. A 3/4 back or theile cab are two such examples.
3) Number of speakers affect tone.
i. A 1 x 12 can get plenty loud but you'll always sound rather one dimensional and 'blaring'. These are great in a situation where you don't want to override a weak sound system or levels are an issue. I suggest every guitarist with a head has a GOOD 1 x 12 such as a 3/4 back or a theile. These are suitable for low volume or practice situations.
ii. 2 x 12. Good middle of the road solution. These suckers sound phatter and project more. The two speakers add a lot of thickness and meat to distortion tones while moving twice the amount of air as a 1 x 12, yielding a great solution for medium volume gigs. If you put the 2 x 12 up on a chair so you can hear it, it should keep up with a fairly loud drummer and sound pretty phat.
iii. 4 x 12. One of these projects like crazy. Two is a wall of sound. These are really great for rock gigs, especially with a loud drummer or when you can't put guitars through the PA. They are also excellent for outdoors, with lots of projecting power. These suckers are cumbersome, heavy, and difficult to move but they really are an icon of rock and roll. Some 212s get close with how big they sound, but a 4 x 12 moves so much more air that they really just can't keep up by comparison.
For a serious gigging musician, multiple cabs with different numbers and types of speakers make for a very versatile setup. For instance, running a Recto with 6L6 tubes into a Rectocab will sound quite different than running a Recto with EL-34s into a Marshall 1960ac 4 x 12.
4 x 12s.
If you want Nu Metal Sag and a bit of a scooped tone, go with a mesa boogie Standard Rectocab. These tend to cost a bit more but they sound huge if that is what you are looking for. The Stiletto cab is voice more traditionally and is very similar to a Marshall 1960vintage except it is darker and more thumpy.
Marshall cabs are decent. Look for the 1960lead (G12T 75s 300watt cab) 1960vintage (Vintage30 240watt), 1960ac (greenback 10 watt) 1960a cabs tend to sound mega scooped while the 1960vintage is more mid heavy and tight, and the 1960ac is woody with more speaker breakup.
2 x 12 rectocabs also are loud and sound great!
http://instrument.jaxed.com/cgi-bin/music.cgi?cat=msg&itm=mesa
Look here or check the local buy and sell to see what you can come up with. It is a buyers market so if you know what you like ahead of time, you should be able to assemble a pretty killer rig!
Mesa 4 x 12s http://instrument.jaxed.com/cgi-bin/music.cgi?cat=msg&fil=4+x+12&itm=mesa&state=&ps=&pe=&ys=&ye=&submit=+GO+
$650 on average.
Mesa 2 x 12 http://instrument.jaxed.com/cgi-bin/music.cgi?cat=msg&fil=2+x+12&itm=mesa&state=&ps=&pe=&ys=&ye=&submit=+GO+
$300 - $400 on average
Marshall 4 x 12 http://instrument.jaxed.com/cgi-bin/music.cgi?cat=msg&fil=4+x+12&itm=marshall&state=&ps=&pe=&ys=&ye=&submit=+GO+