I carry both, they both work fine. Dynaflight '97 is more durable, and easier to work with; 450+ has a little less stretch and creep.
If I were going to invest in just one material, I'd go with either Trophy--basically the same as 450+, but with GORE fiber to reduce fuzzing and a smaller diameter strand--or 8190.
8190 is 100% HMPE (no Vectran, as is in 450+), very low stretch, very low creep, very small diameter strand. This is the material Hoyt is using on their high-end wheel bows.
Between Dynaflight '97 and 450+, I'd pick Dynaflight '97. I'm considering selling my stock of 450+.
Chad