The optic 6 and the 6EXA are really at different levels in almost every respect.
6EXA is an entry level computer radio
Entry level Computer Radios 5/6 channel - approx $90-110
If your focus in on parkflyers, RES sailplanes, aileron sailplanes or glow
planes, these are very capable for the price. In addition to the basic 4
channels they have retract, flap and/or split aileron capabilities. These
make great first radios for the committed new pilot, providing features beyond
the 4 channel "standard" radios at a small incremental investment. For many
pilots, these may be all the radio they will need for years. They will fly
more advanced planes, like full house sailplanes or aerobatic planes, but may
not be able to bring out all the plane can offer.
Futaba 6 EXA -
http://www.futaba-rc.com/radios/futk55.html
6 channels, 6-model memory, Prop Flaps on Channel 6, Flapper using channels 1/6, 1 user
defined mix. No timers.
Optic 6 is a mid range computer radio, by comparison
Mid Range Computer Radios 6/7 Channels Approx $130-160 for the radio.
These radios provide a richer feature set than the entry level computer
radios, primarily in more model memories, more surface mixes and switch
assignability. These radios can bring out more of the capabilities of more
advanced planes and give you set-up options the entry level computer radios
lack. If you have been flying a while on a 4 channel radio and now want to go
to more advanced planes but keep the price "reasonable", this might be the
group to consider. If you are a new flyer with a larger budget, these may be
a good fit. Some have limited split elevator features for larger or aerobatic
planes. Read the manual carefully on this. For example the 7C can operate
split elevator servos, but can not trim them in flight.
Hitec Optic 6
http://www.hitecrcd.com/Radios/OPTIC.htm
6 channel, 8 Model Memory, Model naming, Spectra channel synth option, Change
channel module, shift select, Switch Assignability, flight modes, 2 user
programmable mixes, and a variety of standard mixes.
So, what kind of flying do you plan to do? What is your budget. If you can afford either, get the Optic 6, it is a much more capable radio.