I forgot to note i already have a 3.5 to usb 3.0 drive adapter
Well that should make your decision easy then.
The CM690 II has an external 3.5" drive bay the Sentey doesn't have one.
20.80" x 8.40" x 20.10" - CM690II
21.65" x 8.42" x 20.47" - Sentey( don't know why they say this is a full tower)
The Sentey has stupid 80mm fans on the side panel.
I own the CM690II = very good cable management,roomy,and easy to work in.
Great airflow and good build quality.