WHich would give me better security? TLS or SSL??
The one that doesn't work
If it doesn't work then you won't have email, so will have no email security worries
Use whichever is supported by your server. The server will support one or the other, not both. The two are equally secure. The distinction is that with "TLS" there is a brief readable interaction before switching to encryption, while with "SSL" you jump straight into crypto.
For sending email, if you are told to use port 465, that will likely be SSL, while if you are told to use port 25 or port 587, then specify "TLS" (or "TLS if available" if you are not sure whether the server supports it).
For receiving POP3 email, if the port is 995, that is likely to be SSL. If the port is 110, specify "TLS" or "TLS if available". For IMAP, port 993 is likely to be SSL, and port 143 will use TLS if it uses encryption.