If you have a relatively small setup with a few servers and mostly expect north-south traffic (servers with the rest of the routed network) rather than east-west (across servers), then MC-LAG will be simply and easy. However if you are looking for multi-homing, need scaling for east-west traffic and resilience, then EVPN-VXLAN topology with QFX5120 as leaf (VXLAN gateway) is the way to go.
I've tried to share some useful links you might want to skim through to make a more informed decision .
It depends if you're forming the MC-LAG between two QFXs and the server - in that case, multiple physical servers will need multiple LAGs. Else if you're making a LAG between the QFXs and an access switch where servers connect, then it needs a single LAG from the switch to the QFXs.
Found a sample of each example here, please review and take a call based on your use-case:
@RoutingFrames you should really be having this discussion with your Partner-Juniper sales team, as to best approach, and long term goals. The are various reason to use either 'design', and both will provide the capabilities you are looking for. Your local people should be able to best direct you.
BTW, an even potentially easier solution would be to VC 2 x QFX5120 together; this support if forth coming.