Using 2 GMail accounts at once

I think it would be best just to forward them all to one. If you use a mail client like Thunderbird, download them in IMAP so you always still have a backup on the server if your machine crashes. POP will delete them once downloaded.

"Depends on what you're trying to accomplish.

I chose to just forward all my other gmail accounts to one primary one, allow the primary one to send as the others, and set gmail to send replies using the address used in the original message.

For good measure, I also added a filter to automatically label incoming mail with the address that it was sent to (and you can also have it skip the inbox, if you really want a separate experience)."

"It's a tradeoff.
If you add the account as pop3 you might wait <60 minutes till a mail pops up in the right mailbox because google only checks the pop3 account every 60 minutes.
On the other hand using pop3 allows you to add labels on the mails that go to the second account."