Contrary

[MikeA]

It is a "given" that you should always play VP with max credits, right?
 
Not always!
 
Consider that you may be in a casino that has radically different pay tables for the same game but for different denominations. 
 
For example, at a casino at which I often play, their Video Poker overall generally just sucks and I shouldn't be playing there anyway (but the comps are GREAT!)  Their DDB game at the quarter level is 9/6 which has an ER of 98.981% (5-credits played.)  DDB at the nickel level is a whopping 6/5 which pays 94.675% (5-credits played.)
 
However, if you work the numbers for that quarter DDB 9/6 game with less than 5-credits, you come up with 97.832% ER.  If played for 1 credit you would be wagering the same as 5 credits on the nickel machine yet would be getting over a 3% better expected return even WITHOUT the Royal bonus.
 
Which is the better game?  Obviously, the quarter machine in this case but ONLY if you can avoid getting the crap beat out of you by quarter players looking for a machine to play!
 
Obviously, this is one of the extreme examples, but there is usually some difference between denominations though maybe not as great as that sited.
 
A tighter example might be between 10/7 Quarter Full Pay Double Bonus and 9/7 nickel.  5-credit 9/7 at 99.106% is not as good as 10/7 1-credit at 99.108%.  Yet the amount wagered is the same.
 
It's something to keep in mind if your budget requires that you play at a lower than optimum wagering level.

[shadowman]

Good points, MikeA. You can even go a little further with this if you look at the "cost" factor, that is, turning payback % into actual dollars. There are many times where playing lower denom machines with lower payback will actually cost you less.