No, no, no. The Thundercat is a 4-valve bike (5 didn't fit in the small bore, the 5-valve heads are on 750s and 1000cc bikes). The YZF600 family came out in 94 and the Thundercat was a facelift version, very similar.
The CBR would be better because by 2002 they had an alloy frame and more power, but this is a 'cheap' model because it's one of the uglier CBR600s (in the eye of the beholder of course, but the following model looked like it was from a different era). By 2002 Yamaha were of course selling the R6, a far better bike, or at least a faster bike. In this period the CBR was the bottom of the class for looks and performance.
But year-for-year there was nothing between the CBR and YZF, indeed the whole 600 class was incredibly close during most of the 1990s. Honda are famous for their build quality, but there's really not much in it. I would certainly get whichever bike is in best condition and represents the best value, this is much more important for the bikes you're going to buy.
