Best place to start for sending data from custom forms into Keap?

After reading though the list of items below I have some simple questions:

PREMISE:
Because I want to simply send some data from a custom landing page with a custom form using PHP to collect UTM vars and custom fields from paid SEM campaigns…

Is this a TRUE statement:
A) I should use the infusionsoft/infusionsoft-php SDK to make an XML-RPC call to the API via HTTP POST method to the V1 url using access_token = Legacy API Key here: /crm/xmlrpc/v1?access_token=123abc - because this will make my life easy and it will be around for a long time

Is this a TRUE statement:
B)- I should use use a Service Account Key and V2 of the API because its better and the Legacy stuff is going away one day (which is why its called legacy)

or…
Is this a TRUE statement:
C) Both are true because either could be used, but option A is the best choice for PHP and the low volume usage case we are expecting

I have read through the following:

The simplest and most future-proofed method would be B, using a Service Account Key against our Rest V2 API.