I'll throw my 2 cents in here as a fire protection engineer for over 40 years.
Yes, I agree C02 might be the best if your worried about clean up, but is is also the demanding as far as skill to use in put out a fire instead of blowing all over. Also, there is no residual effect especially when dealing with ordinary combustibles such as wood etc. Before you say, "Yes, but this is an electrical fire", remember when you pull the power (open the breaker or blow the fuse), it is no longer an electrical fire. Depending on what is burning, it is either ordinary combustibles or flammable liquids. Most will not be dealing with combustible metals and then you need a special extinguisher depending on the metal.
My best recommendation is to have and use an all purpose ABC Dry Chemical extinguisher. Yes, it will make a mess; but your chances of putting out the fire and SAVING the building are the greatest.
Also in any case, you need to get training in the proper use and maintenance of the type that you want to use. Get the extinguisher and hang it close by but not exactly on the equipment that your trying to protect. If something happens, you want to be able to get to the extinguisher without putting yourself in harms way. If you have it in a rather confined shop area like most of us would, hang the extinguisher by the door as that is a good place for it.
PS: Also in case of fire, call 911 FIRST and then try to fight the fire. The Fire Departments would rather arrive and help with mopup rather and having you wait until it is out of hand and have to fight a major incident!
Art
AKA Country Bubba (Older Than Dirt)