Do you ever see both options W1 and W2 used?
Not sure if you mean used on the same contract but if you do the answer is know. They are options to choose at tender stage - i.e. which are we going to choose, W1 or W2. It is the same as which primary option do we choose - you can only have one.
In the UK it will always be W2 as in the UK there has to be the right to go to adjudication, which W2 is written around. Internationally where that does not apply the choice would be W1.