I have always felt that IQAS is way better than WES when it comes to 1. Correct evaluation of your credentials 2.The process they follow.
I am not sure if IQAS conducts any 2nd level of verification as done by WES, but with WES secondary verification one can really get stuck where WES says it has sent docs to university while university denies it. So its matter of time before you receive your report. Additionally as
@ailyas2 pointed out, when we decide to go for IQAS, we agree to 20 weeks timelines from AoR