Has anyone bought bulk MREs online? Should I just get Mountain House meals?
Depends what your want or need is.
Mountain House are good for 25-30 years, while MRE's are around 3 years. IIRC. Stored reasonably climate controlled. 75F and under, or therabouts. I wouldn't eat an MRE that'd been in my truck year round after 4 years, unless starving. I would take a mountain house can or pouch stored the same on a backpack trip tho, and likely enjoy it.
Mountain House require water, and boiling/hot water to be quicker/tastier. MRE's can be eaten as is, may not be great, but still food.
Then there is the weight / bulk consideration.
As to where to buy both / either, as in all things, "it depends". We are in Oregon (We'd pass Mountain House in Albany on the way to our old range ARPC Albany Rifle & Pistol Club) so Mountain House are relatively easy to buy / trade. No big bases around, so MRE's aren't as easy to source, but we have in the past.
If your question is in regards to starting a long term storage food plan for your family (good for you, for caring for your family!)? The most inexpensive is to do it yourself bulk bought, split into Mylar with oxygen absorbers, the next least expensive is LDS (latter Day Saints) #10 canned bulk foods. One need not be LDS to shop there, and there are Bishops Stores in about every State IIRC. Great folks too. Those 2 are just the start of a plan, given that they are primarily just beans & grains. You would supplement them with whatever (include Mountain House & corrolary quality freeze dried)-further on that note, run away from anything branded " Wise" "Ready Wise" & most if not ALL multi day "kits".
MRE's do not fit a long term food storage plan, simply due to there shelf life. They are however great for any number of midterm to short term plans, IF you maintain rotation. Things like tornado shelter, hurricane, wildfire evac, week long power outage etc.
IMO...