If you compare ventilation alone, the CM 690 wins, hands down:
(1) 2 fan grills in the bottom panel help with the "stack effect"
(hot air rises);
(2) another important difference is the 3.5" drive bays:
removing and installing HDDs in the Antec is much more
difficult after a motherboard & cabling are installed;
(3) the CM 690 has 2 fan grills in the left-side panel,
Antec has only one;
(4) CM 690 has a fan grill under the CPU socket;
(5) CM 690 has two fan grills in the top panel;
etc.
After that careful comparison, buy the Cooler Master HAF-922 instead!!
http://www.newegg.com/Product/Product.aspx?Item=N82E16811119197&Tpk=N82E16811119197
The HAF-922 improves on the CM 690 and on the Antec Three Hundred.
Note in particular the large opening under the CPU socket,
to facilitate installing proper backing plates for the HSF:
http://www.supremelaw.org/systems/heatsinks/warning.htm
Also, there is an extra PCI slot cover, for adding USB, Firewire
and/or eSATA PCI brackets without obstructing the motherboard's
expansion slots.
Cable management is a whole lot easier with the HAF-922 also,
because the holes in the motherboard tray are larger. We had
no trouble threading numerous cables from a Corsair 750W PSU
through similar holes in the HAF-932:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139006
(no modular cables)
Lastly, the HDD cradles are the same as those in the HAF-932 --
really easy now, particularly after the system is fully assembled.
For an extra $40 USD, you'll never regret the extra expense.
MRFS