141 if your aiming for a career USA
part 61 is something to avoid all together if your intention is to become an instructor
in the FAA in order to obtain hours and later get hired by an airline.
My suggestion, part 61 if you know somebody who can get you in the airlines for sure if not, stick with 141 from PPL all the way up.
Doing a ppl 61 and then an instrument 141 would be inconvienent.
In all though this might just end up costing you a lot more money (141).
Get some good advice from REAL people and not just forums.