This also depends on how you are set to track the values, it's not a completely "clear cut" answer.
Personally, I will only use HIT on my pageName eVars... but I make sure that this eVar is specifically set on all pages and hits.
If you are only setting on the page view, and want the data on the actions as well, VISIT expiry will help with that (the actions will use the maintained value)... but you also run the risk of mis-association....
Think of what happens on the next page if both an action and page view are triggered, and if that action happens before the page view... now you have the previous page' name associated to the action, which isn't good, and the impact could be significant if people have a tendency to click on your tracked elements before the page finishes loading, or if you fire custom actions automatically on some pages (like cookie consent, or tracking signups to notifications, etc)...
The other problem is if, for some reason, the pageName doesn't get set on a page, and you are populating both your pageName and eVar with your Data Element, Adobe will replace a null value in pageName with the current URL, but your Data Element will pass a null value, and the last previously sent value will continue to populate into your eVar, and depending on the issue, that could be several pages back (unlikely, but possible).
The standard pageName dimension always sends on all calls to Adobe, but it's removed after the fact during Adobe processing. However, using the dynamic variable notation, you can set your custom eVar to "D=pageName" which will replicate the pageName value into your eVar, and this will happen before Adobe removes the standard pageName. Just make sure it's added to all rules (page views and actions) and you should be fine.
If you decided to stick with setting your eVar to a VISIT level expiry, you can do so.. but just be aware that there is a potential here for incorrect values as per some of the scenarios above.
