This is the RV-12 forum.
If a 12 is being built as an E-LSA, there is no option to do what you think is better. In reality, either way requires the proper crimper to install the pins.
The low cost crimper mentioned in section 5 of the manual actually works quite well. It is what we use in my shop.
I would never recommend soldering the pins for a connector at this location on the RV-12 unless the builder was highly skilled at soldering and could avoid any solder wicking into the wire beyond the pin (lots of potential for vibration induced wire movement at this location).