The Openreach modem works fine, you pick them up for ~£20-30 from auction sites, but no warranty and no real support. Draytek also works fine, you pick them up new for ~£80, but you get warranty and support.
To be honest, only you can decide.
would there be any difference in terms of Speed, SNR etc, between the two?
or are they equal in terms of line performance?
Looking at MyDslWebStats I can see users with OR modems (HG612) having an attainable rate of 122, 124 and even 137Mbps and an uptime of 127 days so the things looks more than capable.
The above site doesn't monitor Draytek so nothing to go on there. Maybe @Liam_ would have an opinion as I think he's used both on the same line.
Any differences will be marginal and will depend on the cabinet you are connected to. If you are connected to an Huawei cabinet, the HG612 with a Broadcom chipset might possibly be faster than the Vigor with a Lantiq chipset. However, if you are connecte to an ECI cabinet, the Vigor might be faster.
I'm on a Broadcom cabinet with the Vigor 130. The deciding factor for the speed is the line quality and distance to cabinet.
I seem to have quite a good line.
Distance to cabinet approx 350M
Synch is 80/20
Throughput is 79999/19999
Attainable is 104198/34274
So no issues with the Lantiq chipset. A Broadcom router gives almost identical results, still 80/20 and 79997/19999.
Never had an OR modem, thought about getting a couple but decided against used kit and got the DrayTek.