Spikes puts out a pretty much milspec AR. Windham's is a commercial grade AR which to many of us is less desirable. Both work for normal range use, so it depends on your wants and needs. Of the two, I'd go Spikes but don't forget BCM and PSA. Assuming you can find any in stock right now.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together. You'll remember the quality of a gun long after you forget how much you paid for it.
US Army 1966-69, VFW Life Member, Retired Geek