I have a long history with both Quartus and ISE. Between those two tools I agree that I much preferred Quartus. Better integrated, easier to use. SignalTap was a big part of that. Much easier to use than ChipScope.
About a year ago we started a new platform targeting a Zynq device with Vivado. Got pretty far down the development path on a ZC706 dev kit, but due to some pricing issues and limitations of the Zynq silicon (no DDR4, no PCIe gen 3, etc) we jumped ship over to Arria 10 SoC and Quartus Prime. Compared to Vivado, Quartus Prime feels quite outdated and cobbled together. I found Vivado's IP Integrator vastly superior to Qsys, which is a pretty primitive tool by comparison. And the way Vivado handles IP is consistent and very well thought out. Quartus is way behind in that regard. Xilinx is also light years ahead of Altera in terms of documentation (quantity, quality, ease of management with DocNav) and in the availabiliy and quality of reference designs.
As for development communities, as mentioned by sveinse above, this forum is a ghost town compared to Xilinx'x user forum. Especially for SoC designs. I've posted a few Arria 10 SoC questions here and don't think I've ever gotten a response. Xilinx staffs their user forum with a whole team of employees who monitor the forums and answer questions quickly. On this forum there is very little company support. We knew we were early adopters with Arria 10 SoC, but it really feels like we're flying solo. So far the Arria 10 silicon looks awesome vs. Zynq. But tools and support are critical and Altera is way behind Xilinx in those areas. It's not even close.
Back to the title of this thread, there is a lot of hype with SoCs. Both Altera and Xilinx are pushing hard on the idea that any old software dude with no FPGA experience can describe a system in C code, push a few buttons, and voila! Well, it's never going to be that simple. If all you need is a processor and a few peripherals then no problem. But integrating a hard processor with a complex FPGA design on an SoC is not much different than it was with a separate processor and FPGA. In fact in some ways it's harder because the tools and methodology are geared toward the Qsys/IP Integrator approach. That's where hype meets reality.