What is the best way to capture multi select data in Adobe Analytics?

Depending on the length of the potential values, you can use a "List Enabled" prop, to pass all the values with your selected delimiter.

For example:

s.propX = "value a,value b,value c,value d";

or

s.propX = "value b,value d";

If propX is set up as list enabled with comma as your delimiter, each value would be split to its own row in your report..

Note that a prop enabled list can hold up to 100 characters maximum. So if the values you are passing will exceed that characters count, this is a bad choice to use.

The are also 3 list parameters available to you, these are basically like eVars, they can have an expiry assigned to them (default is Visit, but this can be changed for your needs). 

Like the list enabled prop, you can choose your delimiter, but unlike props, lists can take up to 255 characters per item... you can pass as many items as you need. 

The report would look similar to above (assuming you used Hit expiry if pairing with occurrences metric, but you could use ListX Instance to get when the values are set, with a longer Expiry like Visit you can correlate to actions later in the Visit).

For multi-select we generally do not do the list variable approach, which is often a good approach for multiple values created with one action. My Business typically just wants to know which options are being used or which can be dropped because they are not used. How much a given option is being used as an indication of user intent is typically of less interest, mostly because of how we use multi-select in our designs.

Thus, using a list variable is a bit of an overkill for us. We pass the values with a delimiter into a regular variable. We can easily see what combinations of options are used and can use report filtering to see the use of any given option. If we need to get fancy, there is always Excel.