The HRX series Honda models have a NeXite (composite) mower deck with a lifetime warranty. No rust, fading, etc. to worry about.
SmartDrive is a simpler design, where the drive belt is loosened or tighten by moving the control. Reliable and ergonomic, less parts, less costly to manufacture. You can get a SmartDrive on either the steel deck HRR or Nexite deck HRX model. You can adjust the height of the SmartDrive control much like a tilt-wheel on a car (it has five positions).
Hydrostatic "Cruise Control" is pressurized fluid drive. It's a proven design, (in production almost 25 years) and takes a bit more training to get the feel for it. It has twin levers, one to set the maximum speed, the other to adjust the speed from 0 to maximum. Cruise Control is only available on select HRX models.
You really should try both for a few minutes and see what you prefer. Both have their fans and haters!
Key start is great. New models are self-charging (engine keeps the battery charged). That said, Honda mowers are easy to pull start. Figure about $75-$100 more for electric start. It's available on both select HRR and HRX models.
Find a local dealer with this link; call ahead and arrange for a test drive:
Find A Honda Dealer