Dude, it's a pickup. a few kilos on a hard-top canopy wont make that big a difference. It will be more secure and the hardtop looks much nicer.
And theoretically the hardtop would be much more aerodynamic hence less resistance leading to better fuel efficiency.
Few other alternatives:
1. use partially worn out tyres. (Less rubber, less weight, less energy wasted)
2. Remove spare wheel.
3. Don't take any passengers
4. Remove the AC compressor (less weight plus less strain on the engine)
5. (optional) Remove the doors, (saves you weight, and eliminates the hassle of having to open and close the door everytime you get in/out.)
Edited by Watchman, 11 September 2013 - 11:18 AM.