I recently went through a ton of research in buying a new FF in $300 price range. I'll summarize my conclusions:

Common to both units:
o Gps
o Sonar
o Down Imaging

Lowrance Elite 4 Chirp Versus Humminbird Helix

Lowrance Elite 4 with Navionics ($330)
Pluses
+ Chirp sonar
+ Navionics+ Chip for only $30
+ Create your own maps (Insight Gensis)
+ Familiarity (I've always used Lowrance)
+ Transducer installation (Holes already drilled for Lowrance)
Minuses
- Screen Size
- Insight Genesis $99 subscription fee to download maps to unit (viewing online is free)

Humminbird Helix (~$300)
Pluses
+ Screen is awesome (big, nice resolution)
Minuses
- No map chip ($200 additional purchase)
- No chirp
- Can't create your own maps

So it comes down to what features you like. I am really excited about Insight Genesis that is pretty much what sold me. To generate your own maps with Humminbird you have to get a much more expensive unit (which was much more that $99 subscription fee).