You have a couple different options...Take a look at how the regional maps are broke down on the Navionics website....http://www.navionics.com/en/hotmaps-platinum-1
IF you stay in any one region, take a look at either the Hotmaps Platinum or the Nav+ regions card(just came out), the main difference between the 2 will be the Nav+ covers salt and fresh water but does not have the 3d or google overlay options that the Platinum card does.
IF you cover more than one region, I would recommend the Nav+ card. It comes preloaded with all of the US for immediate out of the package use, but in order to achieve better mapping you would need to plug it into your computer and purge the card, which will then ask you to draw boxes around the areas you fish. This allows you to make a completely custom mapping card without boundaries just for lakes you fish. If you keep the yearly $99 update renewal up to date(comes with 1 year free on all cards) you can add or remove lakes as you wish. If you do not keep the renewal up to date, you do not lose any info, you simply can not add or remove things to the card. If you have any other questions, feel free to ask away or shoot me a PM.