So I just discovered this and thought I would share it with you all. If you're as bad as I am this will be a godsend.
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| The larger maps with more points give more XP from the capturing bonus! | 
Make a private Seize Ground server and capture all the points.  That is all.
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| About 4 minutes for 1050 XP. | 
I was struggling to get 500 XP a match working my way up through the weapons you unlock. After discovering this much easier way to get XP I had my thunder hammer in 15 minutes, and seriously, who doesn't want a thunder hammer?
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| I sucked as an assault marine till I started swinging around this bad boy! |