I've been the perfect trifecta...
I've been a SAHM... when my kids were are 4, 2, 4mos my dh lost his job. So I got a job at my oldest's preschool.
So I've been a preschool teacher too... but never to my own kids
And now they are in grade school (and dh is gainfully employed) I work p/t at target while kids are in school. I have no idea if that disqualifies me from SAHM status... but whatever...
....
With that varied experience as a momma, let me tell you you can have a good daycare experience or a bad one, and sorry to say, a good vs bad SAHM experience too.
Now I am sure all the SAHMs here are super moms and do no wrong.

But I am not perfect.
As a SAHM we had great enriching days yes, but we also had days when we never left the house. My kids would be expected to entertain themselves (or gasp! watch TV) while I did housework. They ran mundane errands, and sitting in the shopping cart was not all that exciting thankyouverymuch.
As a preschool teacher, there were NO CHORES! We had to clean up our own messes, but food was prepared by other staff, cleaning was done by the cleaning crew at night. We could (and did) spend our hours learning, playing, interacting, 100% child centered. I'm sorry but (for me) that wasn't possible as a SAHM to do day in-day out.
As a daytime employee of Target, I see my fellow SAHMs drag their toddlers in... Pleading for them to sit still, not run around, no you can't have that toy (even though they let them chew on it... ewww) Screames, screeches, melt downs hissy fits. Kids are over-tired, bored, even if mommy is *trying* to make it a learning experience. Let's face it, mom is just trying to get through the day. Tomorrow might be some great playdate, paint, extravaganza but a SAHM can't keep that up every minute every day. The shopping has to get done, the laundry has to get washed, the floor has to be mopped.
Anyway, daycare has it's positives too. As a daycare teacher I was free to spend 8 hours of my day in fun. The same can't be said for every day as a SAHM.
Of course, YMMV. Some of you I'm sure are more awesome SAHMs than me...
Live and let live. And if you've been blessed to get to CHOOSE sahm vs daycare, consider yourself blessed and stop judging on your fellow mommas...