I have both a Wiz and Dingoo A330. Both are nice little machines. If you buy a Dingoo, in order to get the most out of it, you have to install Dingux, but after that it has many great emulators. The native emulators on the Dingoo are good to below average, but Dingux fixes this issue. The controls on the Dingoo, especially the direction button, is very cheap, so you have to push it more exact and be careful. There are no volume control buttons, this is done through the software. If the Dingoo crashes, you must use a needle to push inside a pinhole to reset the machine, as you cannot turn it off, or press any buttons. It is a cheaper machine, and can run every emulator decent enough.
The Wiz costs a little more, but seems much sturdier. All the emulators I have tried seemed to run full speed, with the exception of PSX emu, which doesn't fully function. The volume controls come in handy, and SNES emulation is much better on the Wiz compared to the Dingoo. The Wiz doesn't seem to crash as much as the Dingoo, if it does, you just turn it off, and back on, no big deal.
I use both of them to play mostly Atari2600, Genesis, Mame, NES, and sometimes Atari800, and a few others. If you can fit the Wiz in your budget it is the better machine, but if not, you can be just as happy with the Dingoo.