regular sonar or down scan?

Don't expect to see fish with Down/Scan/Imaging; while it may show specs or spots that may be fish, the main purpose is to give better detail of structure/habitat directly beneath the boat.  Sonar may show a blob of color(s) on the screen and the scan/imaging will draw it out for you, seeing little fishy pictures or arches (if you prefer), is better done with sonar.
 
Some food for thought, if thinking Garmin, confirm the delivery date before you order.  I cancelled twice because Garmin keeps pushing the availability of their products back.  Also, check what maps of lakes are available through Garmin, I understand you can no longer use maps produced by others.  Updates, if available, may not be to your liking either.
 
Just bought a Humminbird Helix7 and I'm having a ball with the imaging, almost haunting to see what lays below my boat at times.
 
 
PS. Now that I have one of the more sophisticated fish finding habitat locating machines on the market, I still don't catch fish........ but I look good!

BTDT, have you ever considered adding a hook to the end of your line?

Looking at a Lowrance color model. Already have a stand alone marine gps, so only need a FF. Thanks for the info BTDT.

Guess there's a reason why downscan is so much cheaper than sonar. Whichever you decide to get, get the biggest screen you can afford.

The sonar portion will show fish as arches or fish pics., the Down Imaging will show tiny white specs or dots which could be assumed to be fish.   Sonar will mark fish sending the pings down in a inverted cone. Down imaging uses a thin slicing/sweeping style of beam that will print a more detailed picture of what will be found beneath your boat, structure wise.  You can, split the screen on the Helix so you can see speed/temp/etc, sonar/GPS and, DI at the same time.  With sonar you may see a glob of something on the bottom along with arches or fish pic. and the DI will produce a picture showing what the glob is, be it, a crib/tree/sunken boat/etc but, may or, may not show fish as tiny dots.
 
Sonar/Down Imaging is available without GPS but I'd, squeeze the budget if necessary to, get the GPS and a map of your favorite lake, it's awsome.
 
Helix 7 DI has all the features I have except for the Side Imaging which, if your budget allows can be an advantage. 
 
Just learning all the features and settings myself, just wish this stupid wind would go away so I can go and play with my Helix.
 
 
Sending a PM where you might like to compare prices and can find some research info.