Match bullets are better (more accurate), and they are *consistently* more accurate. Any decent match bullet will be able to shoot 1/2-MOA or better at short to mid range (100-600 yards/metres), and should be able to shoot 1-MOA at long range (900m or 1000y).
BTW there are match grade FMJs, but I know that what you're really asking about is not "FMJs" per se, but el-cheapo FMJs.
Bulk FMJs are *much* more variable. You can usually count on them to shoot 5MOA or better at short to mid range (100-600m). Some of them will shoot quite a bit better than that, some will shoot 2.5 MOA or even 2MOA.... but not _reliably_ so. The same ammo fired in another perfectly good rifle might print 4MOA; or, the next lot of the same FMJs might be 3-5 MOA.
Good match bullets loaded into ammo that shoots very well in my good rifle, will almost always also shoot very well in your good rifle.
Bargain FMJs that happen to shoot well in your rifle, might or might not shoot well in my rifle.
At long range (beyond 600m), group sizes from "cheap" bullets will often open up more quickly than groups from good match bullets.
Having said all this, there is a time and place for all of these things. If you are shooting an accurate rifle, in an accurate manner (say, rested with a scope), your shooting performance will be hurt by using inaccurate ammo.
If you are shooting a rifle that isn't particularly accurate, your accuracy might be hurt little to none by using a cheap bullet. My Garand shoots 4-5MOA groups at 100, whether I use el-cheapo bulk FMJs or whether I use the very best handcrafted match ammo I can make.... so guess what I load?
If you are shooting a rifle in a manner that isn't particularly accurate, for example me shooting standing (!!!), using ammo that shoots 2-5MOA might not be noticeable and would therefore be a very good choice.
