I personally don't think you can argue that this one is better or the other. I think it's a matter of experimenting. For example, my Draytek was worse on my line than my Fritzbox (both Lantiq, though different types) and I noticed no specific difference between Zyxel and Fritzbox on my poor line, so using the latter, even though I'm connected to Huawei.
However, a number of people swear by 'matching' the chipset of the modem to that of the exchange. Not sure how they reached that conclusion, as a number of factors could potentially affect a line and its performance (heat, rain etc.). I'd say only lab tests (in controlled environment) would be the only way of confirming whether matching the chipset to the exchange helps.