Settlers and 99% of other games run in native mode (AGA). There's a switch in WinUAE/Display settings that enables to run this mode in fullscreen too.
Press F11 while the emulation is runnig and enable "Full-screen native modes" option. Or change the settings before you start the emulation and SAVE it to "..YourPath..\AmiKit\WinUAE\Configurations\AmiKit_v1.UAE" and "DEFAULT.UAE" in the same location. This way AmiKit will always display native modes in full screen.
You can also set the refresh rate of native modes to "Every frame" however this is not recommend to use regularly since it can slow down the boot process of AmiKit.
You might also try various filter settings in WinUAE/Filter section in order to enchance the quality of Amiga gfx. For more information refer to WinUAE manual - just press the HELP button in bottom-right corner of WinUAE GUI.
Enjoy! :-)
