Since the introduction of the Web Client new features to vSphere would be available only through the Web Client, with the most well known example of VSAN. The performance of the Web Client was not great at all which made it a big obstacle for using the Web Client instead of the old vSphere C# Client. Because of the availability of new features only in the Web Client, for me the choice to use the Web Client was forced but over time I learned to use the Web Client in a usable and relative fast way.
With the introduction of vSphere 6 the vSphere Web Client has been improved in terms of usability and performance. Working with the Web Client is now on par with the old vSphere C# Client.
The continuous improvement of the Web Client makes it really nice to work with and it only gets better. Improvements such as the VSAN Health Plugin and fully functional vSphere Update Manager integration makes the Web Client the tool for managing your vSphere environment.
The only thing that was bothering me was that I still needed to use the vSphere C# Client when I wanted to manage a vSphere host directly. Luckily, a fling has been released which provides a HTML 5 web GUI directly on the host. The ESXi Embedded Host Client is a VIB that needs to be installed on the host. After installation the host can be managed through your browser. I like it very much, almost all tasks can be performed and the developers are always looking for feedback to improve it. Input is appreciated and if possible integrated in new releases of the Embbed Host Client. An example of this is the offline bundle used for Update Manager and Auto Deploy configurations.
I can only say one thing, and that is to use the vSphere Web Client and Embedded Host Client!
Disclaimer: I haven’t used the Web Client bundled with vCenter Server 5.5 Update 3 which according to the release notes should also be on par with the vSphere C# Client on performance.