Regarding selection of appropriate board for application development

No. It all depends on what level of customer you are for both Altera and Xilinx:

If you are a Tier one Customer both will provide direct FAE support. If you are a little guy, outside the Bay Area like myself, your first line is the Altera mysupport or xilinx support web interfaces. Which for both is varied in how good it is based on who your get. With Altera, Arrow also has their own FAE's to support for you. (With Xilinx it's Avnet). Unless it's a common issue they may or may not be able to directly support you, but they are another resource with a backdoor into the factory support structure. So they can and will push your issue thorough the support hierarchy.

My experience has been for a small company, this works better with Altera. I'm part owner of a contract house that has both large and small customers. Some customers are ALL Altera, some are ALL Xilinx. I personally like the Altera tools better, and have better luck with their support. But that being said the Zynq caught Altera flat footed, and they lost many designs because they were in market first with a good SOC design platform. Altera has now caught up, but they were late to the game.

Xilinx seems to be strong in the Tier1 space, because they put more focus there.

Tools side, QSYS beats the pants off of the Xilinx tools for SOC integration, and SignalTap is much easier to integrate that ChipScope for debugging.

But Altera still has nothing to compare to FPGA editor for fixing or debugging minor issues by hand. (Especially handy if you have multi-day build times on a large design)

Pete