I think the substantial advantages of the vista hcx over the 60 csx are 1) lighter and smaller and 2) longer battery life. For a hiking GPS, either of those can be important. the 60 csx may have slightly better GPS performance, but the vista hcx is good enough that it may not matter in real life situations (It won't lock in my office, but always has on the trail). I am not thrilled with the joystick interface on the vista, it works, but is awkward, and particularly tricky when biking. I also find that I regularly push buttons and the joy stick unintentionally, this doesn't matter or effect anything, but it does happen a lot.
The differences in rated battery life are 18 vs 20 hours--not enough to be an issue, IMO. Either will run for a full day on a single set of batteries. (These numbers may include using battery-saver mode. I dis-recommend its use--it decreases the accuracy and increases the probability of losing lock.)
The display on the 60CSx is larger and has been highly praised for its visibility in both sunlight and by backlight. I don't know if the HCx is as good. (It might be worth comparing them side-by-side.)
Many joysticks became unreliable on the original eTrex Vistas, hopefully this has been fixed for the HCx.
The optimum orientation for the eTrex series is horizontal, the optimum orientation for the 60 series is vertical. While I try to position my 60CSx vertically in the top of my pack, I've had no problems if it has shifted into some random orientation. Hopefully the HCx is also sensitive enough that sub-optimal orientation doesn't cause any problems in the field.
My guess is that many if not most users will find the HCx to be adequate for most of their needs. (FWIW, the 60CSx came out well before the HCx, so the early adopters had only the 60Cx and 60CSx to choose from.) It would certainly be adequate for most of my needs, but there are times when I use features of the 60CSx that are not available on the HCx (eg external antenna).
If Garmin is coming out with a button interface 62, that would be worth a look. My guess is that the vista hcx will be much cheaper, in the $200 range.
The current MSRPs are Vista HCx: US$299.99, 60CSx: US$399.99, and the 62s: US$499.99. There is also the reduced feature 62 for US$349.99. (All MSRPs from the Garmin website.) We should also note that the 60CSx and HCx have been available for a number of years and are much more likely to be discounted, while the 62 series is new and discounts will be harder to find.