Re: what's better
In different areas which is better will be different.
The coins that fill coin machine bags are directly tied to a single location and the coins that fill boxes come from a much wider area (the area the area serviced by the armored service).
So a lot really depends on the location and the mix of people who cash in their coins at a particular location. If a particular location has a lot of other CRHers that use the machine you are buying from to cash in.....you will have probably not have good luck there. On the other hand, if people using the machine tend to be either older people who just don't care or people who are ignorant about older coins...you will probably do well there (at least sporadically).
Getting boxes is essentially the same as taking a random sampling of coins from a variety of different locations and/or banks which means sometimes you will do very well and other times very poorly for exactly the same reasons as bags.
Now whether bags or boxes are better for you personally will just depend the particular location you are buying from.
My advice, try both for long enough to get some reliable statistics and see where you do better and continue using that method.
Also whether a machine rejects certain coins or not depends a lot on the type of machine and its calibration settings. Also, just because they might reject some, doesn't mean that they reject them all. I am constantly told that the coin machines reject Canadian (dimes and quarters) yet I ALWAYS find them in the bag and those should be the easiest to reject because they are magnetic.