It's obvious that most profitable for us is to bet big for value and small as a bluff. The only problem here is that this is highly exploitable (unbalanced) play. If (and only IF) we want to prevent our opponent from exploiting us by folding to our big bets and calling small bets we should balance our betting range by making our sizes less different. Degree to which we want to balance depends on a degree of which our opponents are capable of exploiting us. To balance we can make our bluffs bigger or make our value bets smaller (or both). Which way to go depends on your whole betting range. More combinations of value hands we have in the range - bigger our bets should be and opposite to make our whole betting range as profitable as possible. It means if you're playing tight you should use bigger sizes and if you're laggy your betting range is weaker (more bluffs in there) and smaller sizes would be more profitable for you.
You shouldn't change your bet sizes according to your actual hand cause it would give away information about your holdings, but change it according to your range and your opponents ranges.
These are the questions to ask yourself when choosing the bet size:
- How balanced I want to be?
- What's my range in this spot? How strong it is?
- What's my opponent(s) range in this spot? How strong it is?
- How much I want to bet with my whole range?