So what week would be best to avoid Mardi gras? Last week of february or 2nd week of March? Won't the spring breakers be there 2nd week of march?
I can't speak to February but my family typically goes over Spring Break, Thanksgiving, or Christmas because DW is a teacher, and we are not going in the heat of the summer so that leaves those other three times.
We have probably gone over Spring Break at least 3 or 4 times now stretching back several years and while it is busy, we always feel like it isn't that bad. Thankfully where we live in Texas, Spring Break is usually that second week of March which is usually a bit earlier than the rest of the country. For example, we have family in Louisiana, Ohio, WV, and Washington state and their Spring Breaks have never once lined up with ours. The end of that week is definitely busier than the beginning, I can tell you that much. We are even going again next year, arriving late on the 7th through the 15th or 16th (departure date TBD).
Even with the crowds, we have been able to ride GotG and RotR, via virtual queues without purchasing ILL, for what it's worth. Tron wasn't open last time we went.
Probably my biggest advise about going at that time of year is really watch the forecast and still pack a few different layered options, and if anyone in the group has allergies make sure to bring your meds. We have had days with highs in the 50s and then in the upper 80s/lower 90s on the same trip. While we have gotten some rain I will also add that, historically, it has been pretty minimal in March. As for allergies, it's during the Flower and Garden festival at Epcot and while it is beautiful to look at, if I don't take something for them my allergies will flare up fast.
Whatever you decide, good luck and enjoy the trip.