Out of those 2 options I would go with the Cannondale, but that's personal preference. Both are good bikes. Giant has probably the best warranty and back up in SA, but the Propel is an extremely rigid Aero frame. So comfort wont be as good as you first 2 options. The Giant TCR would be a better option IMO For what you want the bike for why not look for a Cannondale CAAD 12 Aluminium frame, but certainly the best in its segment and as good if not better than most carbon frames. Buying used will always have its risks and frame warranty normally doesn't apply to the second owner. There are a lot of good value for money bikes around, maybe don't limit yourself to just 1 or 2 brands. In saying that, try and buy something with good backup in SA. Giant, Silverback, Merida, Trek, Brands like that.