Thank you guys so much, antpools' looks pretty promising, viaBTC is congested way too often these days
All of these services are congested. Too many people are either trying to get away with fees completely and get free services to accelerate it or are making a mistake inputting their fee. I imagine all of these services will eventually convert to pay only, or offer to do a limited amount each day.
There's also loads of people exploiting these free websites over in the service section in order to gain trust or Bitcoin.
You're right, I've seen people "providing free acceleration services" all over the international forums (as I speak Portuguese, Spanish, and some French) and indiscriminately asking for tips.