V Trout, Here are maps from my perspective. Before I start there is something you should know about areal photo overlay and that is the date the photo was taken. This is not mentioned by any of the manufacturers. With the aggressive coastal erosion you will have some degree of inaccuracy with the overlay but not as bad as the base maps that come with the units.
Standard Mapping
http://www.standardmap.com/
pricing $80-$399 depending on Map.
Areal photo overlay, no depth. I have the E55 Marsh Island, Vermilion Bay HDS card and it is good but tends to grain out when you zoom down. 1st pic is from my HDS7.
Legend Cartography
http://www.legendcartography.com/
Pricing $199-$229
Areal photo overlay, no depth. I cant comment on this card but I would assume that it would be comparable to the standard map.
Navionics
http://www.navionics.com/en/
Pricing $199-$349 plus $99 if you wand updates.
Nautical chart type overlay with depth. Navionics is nice and is update able with a subscription which means you will have fresh information but you will loose detail of smaller bayous etc. This is made more for maritime navigation and the big bass lakes, but it is handy since it shows depth. YOu can go to their website and look at the webapp and see what their map looks like.
Now the depth part gets tricky. they collect depth data from subscribers that record sonar data when data is uploaded they update the map and you can download the new version. I have heard this can take up to 6 weeks though. subscription is usually $99 a year. I have recorded alot of sonar data and know some depths are not that accurate.
the good thing about Navionics is you can get the app for your phone for $5 or $10.
Lowrance Nautic Insight
http://www.lowrance.com/en-US/Products/Mapping/
Pricing $99-$159
Lowrance is carbon copy of Navionics but a little cheaper. Through Insight Genesis you can upload sonar logs and create custom fishing maps.
So as you can see you have a bunch of choices and they are quite expensive.
There is a way to create your own but it takes a bit of computer work to pull it off.
I faced the same choices as you did but went a different route. I made my own photo overlay for free thanks to google and purchased map making software. Now I record my own sonar data and write my own maps. the best part is the photo overlay and depth map is less than 2 years old so i have the freshest data available.
I have offered the depth map to anyone who contributes but have only received 1 sonar log to date. Not sure why...
With the dyn-o-mite fishing in VBay I will be reluctantly breaking off in the spring and start mapping Big Lake.
Hope this wasn't too long but with the fishing being slow we all need something to read.
Below are pics from my units
1st - the standard map on my HDS.
2nd is the same area on my HDS 12 with my overlay and contour map.
3rd is a zoomed in shot.