I can't really say who might have the better part. Two advantages of buying from an Alfa parts supplier are 1) perhaps a better chance of getting a part that really fits vs a part that can be made to work & B) supporting an Alfa parts supplier might help keep them in business.
One thing to consider when working with our old cars is the age of the wiring & connectors. When they were new the wires/connectors/etc were plenty adequate for the designed electrical loads. After many years a bit of corrosion, looseness, arcing, age, etc hampers how well the electrons can flow. This reduces the efficiency of the electrical item and
that can shorten their life. It is a good idea to clean all electrical connections, make sure crimps are tight, insulation is intact, wire strands are not broken, etc. If you are willing to learn an easy but useful skill try Googling 'voltage drop test'. Here's some info my brother wrote about
Voltage Drop Testing (but first you have to answer
the prerequisite question...)