I agree with the above posters that whether you do your private under 141 or 61 doesn't really matter. I don't think that many people manage to get their private certificate in 35 hours (141) nowadays anyway.
If you do your instrument rating under Part 61, you will need 50 PIC cross country hours to be eligible for your IR checkride. I imagine you'll obtain around 5-7 of those hours throughout your private training and probably about the same amount during your instrument training. That leaves you with 35-40 additional xc hours required. Obtaining this time can be fun, and will make you a better pilot, but it may be more expensive (141 does not have such a requirement). However, splitting the cost of this time with another student by putting one of you under the hood, will help reduce costs.
When you are ready to pursue your commercial certificate, I'd suggest examining your TT. If you have less than 130 hours TT, it may be more cost effective for you to enroll in a 141 program. To obtain your commercial under 61, you need 250 TT; whereas under 141, you just need to complete their 120 hour syllabus.