If you use PROC IMPORT and need further data transformations, then you have to pass the data 4 times. You could do it with two passes by combining the data transformations in the same data step as the INFILE.
Beyond that, IMPORT is usually easier to set up and INFILE provides more control. If I were reading 10 GB, I'd go for control.
What is your SAS experience level and how complex is the input data? Is the list of input fields and their content consistent throughout (or at least the first "nn" rows) to use with PROC IMPORT? If you are to code and support the INFILE processing method, you will have the ultimate flexibility with defining, validating and shaping your resulting SAS file. These are but a few of the considerations to make a reasonable decision.