i'm a quartus user. Recently, i have to use xilinx tool to synthesize and simulate. but, i'm really confused because there's a lot of thing i didn't know about xilinx tools.
as a general difference, Xlilinx ISE has been assembled from several OEM tools, the same e. g. with Lattice. Thus operation isn't as covenient as you're probably used to with Quartus. But don't panic! It's basically understandable, they have help files, examples, tutorials and such. As far as no particular device resources are involved, you can also perform HDL syntax check and functional simulation in Quartus.
XIlinx is a powerful FPGA Design tool if compare to ALTERA. If you're expert/advanced FPGA designer, most probably you wil think Xilinx is no.1 compare to ALTERA because you have more control on your design and PlanAhead is actually a good Place & Route tool where it provide the best routing for you if you master it...
Quartus syntheize tool is giving very close result as Synplicity
Altera design constrain using *.SDC format (which is standard de-facto in ASIC industry) which means when you constraining your FPGA you taken trace delays on PCB in consideration, not like Xilinx when you have take timing report and incorporated in PCB
from code changes to FPGA only two mouse clicks in Altera, Xilinx way more