for me it's on a per map basis. Mirage/Cache/Cobble I prefer the A4 because its usually close/medium range. For Train/Overpass/Cache I need the A1 because I cannot use the A4 at long range, I feel like its impossible.
I really hate how Valve removed the ability to buy both with buy binds. Everyone complaining about ladders and hitbox glitches and no more darude sandstorm during warmup but this was the worst "fix"
edit -
http://www.gfycat.com/WetFeminineBrocketdeer
man they fucked it up more than I imagined. you can't even disconnect to switch weapons now if that's real