I'd go with the Define S (even if the S340 looks more elegant), for the following reasons:
The S340 can have: 2 front 140mm fans, a top 140, and a rear 120. So 4 fan slots, while
Define S can have: Three front 140s, 3 top 140s, a rear 140, a bottom 140, and a side 140 (if you don't want a...