When acquiring the initial filament for my school I purchased several varieties. At the end I was a few dollars short so swapped two of the rolls for a slightly cheaper PLA plastic filament. This was $20/kilo as opposed to the $25/kilo.
Not a tragic mistake, just a big one.
I initially used the cheaper PLA for my prints to get the hang of printing, and eventually switched over to the higher quality plastic. What a huge difference I noticed in the prints! Everything came out a lot smoother and most consistent.
The other issue I had was filament breaking. This would occur even with the filament environment controlled. (See the Troubleshooting page under “General Information & Suggestions”) Over one reel of filament there were over a half dozen failed prints. The filament would break, but the printer would continue running, leaving the print only partially completed. What a waste. Lesson learned.