How do you pick a favorite plant? LOL I have MPS (multiple plant syndrome) so I have many favorites. If I HAD to pick just one, I think it would have to be amazon sword. They fill in tanks nicely, provide lots of hiding, break the line of site, and just grow really well in my tanks.
After that, I really like my ludwigia repens because they grow so well and I just keep trimming and replanting to get nice full stands throughout all my tanks.