Let me be the first to say welcome to the forums! How has the PPL training been?
...but also let me be the first to NICELY advise a use of the search feature to view any of the many threads over each of those schools. They are among the most popularly discussed ones (especially ATP) and you will find a plethora of information on them.
Given that you HAVE been reading, I'll give you a cliff notes on most of those big 141 "Pilot mill" schools.
Good: They are total immersion, you eat live and breathe aviation because at the rate you go, you have literally time for nothing else. You do in 90 days what most people (including myself) did in 2 or 3 years. You get LOTS of multi-engine time (ATP) and that is very difficult to get otherwise. TT builds really quickly with entry level 91 jobs (Flight instructing, banner towing, jumper dumper, piper patrol, etc). A lot of them have good bridge programs with the airlines. Airlines are hiring. ATP also will hire you straight as a CFI which looks good on a resume and is a nice way to build time.
Bad: They are total immersion, you eat live and breathe aviation because at the rate you go, you literally have time for nothing else. You do in 90 days what most people (including myself) did in 2 or 3 years. Yes, those points are both good AND bad. It is a lot of money right up front. However, I ran the numbers, last time I looked at ATP for what you got, the rates were not that bad. The problem is some schools that ask for money up from go belly up without a warning and you are out money. ATP seems pretty solid but so did PanAM. Quality of training: Many people argue that you are taught for a checkride and receive very little other training. Also, especially on these boards, there is a negative stigma surrounding these type of schools. I don't think it would really set you behind others in job hunt, but be aware some people thumb their nose at these schools.
Well there you go. Hope that leads you in the right direction but like I said, these schools are discussed much more in depth than what I posted. Good luck!