Hi, I'm coming from a software background and understand the way compilers produce assembly from a high-level language. But not so for VHDL. I therefore often do not know what VHDL to write that's most efficient. For example, I'm currently creating a graphics card with VGA output, and in 1bpp mode, I want to output white if the bit is set, and black otherwise. I came up with two different approaches (the DAC has 4 bits per RGB). First:

	o_video_r <= s_attr(0) & s_attr(0) & s_attr(0) & s_attr(0);
	o_video_g <= s_attr(0) & s_attr(0) & s_attr(0) & s_attr(0);
	o_video_b <= s_attr(0) & s_attr(0) & s_attr(0) & s_attr(0);

Second:

	if s_attr(0) = '0' then
		o_video_r <= "0000";
		o_video_g <= "0000";
		o_video_b <= "0000";
	else
		o_video_r <= "1111";
		o_video_g <= "1111";
		o_video_b <= "1111";
	end if;

So what would be considered the "best" code? Also are there a bunch of guidelines for writing VHDL to be found somewhere that focusses on best-practices?

I would go for the second. The difference in efficiency is minimal if any, and the second is much more visible on what the purpose of the design is and makes it trivial to change the values if you want it to map to any other values.