I’m not at either and I am waiting on my class date at my new airline in June. However, I had the same goal for a very long time before I learned about ACMI. FedEx and UPS are definitely the most recognized freight carriers but there are so many options for flying heavy cargo that would be potentially much easier to get hired earlier in your career.
Also try to get away from referring to regional airlines as “using them to build time”. Even though this is the case for most of us, people don’t really like to hear that especially when you are hoping they will hire you. Trust me I made that same mistake early on as well.
Either way, to get to FedEx or UPS you will most certainly be going after a couple thousand hours of flying and not without jet time so it helps to focus on the shorter term goals to keep from losing your mind.
the best way to get to know each airline is to find an active pilot that works there and talk their ears off. Im sure you will find someone here that can help with that. I personally know and have flown with 2 separate FedEx captains recently, one absolutely hates it and the other loves it… I thought that was hilarious as they have both been there for 20 years.