1 with all the DLC is better. In the end if you were not a fan of D1, D2 will not win you over either. You may still find entertainment like you did with D1.
I do not know how many people still play D1, so some activities may be a pain or impossible to do now.
Vanilla D2 may be so cheap because there is currently $30 of DLC out now with another $40 DLC coming in Sept that will require all existing DLC.
I think there is a trial of D2 you can download. Maybe try that first.