If you only buy one, the Companion has the 30 amp twist lock plug and one 20 amp plug; but the output is the same as the Standard. And, it costs $100-150 more.
Again, if you only buy one, the Standard has two 20 amp plugs and costs $100-150 less than the Companion.
If you buy two Standards, you save $100-150 over getting one Standard and one Companion. However, you don't get the 30 amp twist lock plug; and a 30 amp adapter will cost extra, probably close to what you saved by not buying one Companion.
If you buy two Companions, you get two 30 amp plugs, but you can only draw 26 amps continuous load; and you paid $100-150 over the cost of one each, and $200-300 over two standards.
Thus, if you are only buying one, get the Standard. If two, get one of each. By the way, there are 50 amp kits that will join 3 EU200i's.
One EU2000 will run about anything you have except the air conditioner, although probably not all items at the same time. Some people have reported running their air conditioner; but it sounds like there is some risk of damaging the air conditioner and/or the generator, so this probably isn't a good idea.
Please note that this summary is from studying the owners manuals and discussion threads on this site, and not from practical use. (I did a lot of reading before purchasing a couple of weeks ago.) I'm sure others will provide info from their personal experience, which was a great help in my purchase decision.