Are you 100% sold on one of those two units? Wayne is right in my opinion that if you fish you still need traditional 2D Sonar. DownScan is a big deal and I can honestly say that I use both equally and need both equally.
Secondly, if I'm not mistaken, neither unit has GPS and mapping? This is very, very important o me for several reasons. One, with mapping (and I know I'm a Navionics guy), I would have no idea where to first find fish and/or fish holding structure. I think this is an area Wayne would agree with me heavily as he is one of the leaders at creating lake maps with the new technology that has hit the scene, such as SonarCharts.
Also, when you do find fish you'll want to save a waypoint so that you can catch crappies off that brush pile for years to come.
Lastly, screen size may not seem important to you now and after working many Lowrance booths at shows I've heard it a thousand times over and myself included was guilty thinking I didn't need a larger screen but truth be told no matter if you go HB or Lowrance 85% of first time buyers go back and buy a larger unit within a year of purchase. This is simple and as you learn more about the unit and show success on the water, you'll want to be able to get the best detail and function you can afford.
If your budget is set in stone than forget all this and enjoy. However, if your looking for input to help you make a educated desicion, take what I say into consideration.
I'm not saying you need to run out and buy a $3500 12" Touch Screen (even though I wouldn't trade any of mine in for anything) but there may be some better options available to you or only a couple more hundred and will offer you almost everything you could ask for.
My recommendation would be the Lowrance Elite 5 HDI. $499 straight up but I've seen them cheaper from time to time. This gives you mapping, 2D Sonar and DownScan, all with a slightly larger screen.