Just wondering: in what way do you think Vivado is better? Do the tools also build a design faster or is it just the user interface?
1. It works in Win10 Pro without nasty hacks or virtual machine.
2. Xilinx provide Microblaze softcore for free for all 7 series devices, which is not the case for S6.
3. I really like visual designer because it helps to visualize the system and how each parts of it are interconnected. Staring at HDL is nowhere near as "visual".
4. SystemVerilog support with some advanced IPs like AXI Verification (which is written entirely in SV) which makes developing testbenches for AXI-capable components MUCH easier (issuing a transaction in a testbench now takes only few lines of code).
5. "Cleaner" and IMHO more logically-organised GUI where controls are mostly where you expect to find them.
7. Most importantly it's not "abandon-ware" like ISE is.
I also like 7 series fabric because it's faster than S6. My initial detractor was BGA only package options (S7 was initially announced in TQFP-144 package, but it got cancelled somewhere along the way), but once I realized that DDR2/3 only exist in BGA packages as well, and got over my fear of them, I can now select a device based on what kind of capabilities I need for a specific project, not on what's available in packages I can work with.