I'd go with GLA. The CarbonDoser makes a constant ticking noise. You can muffle it with a towel, but in a quiet room you'll probably still hear it. The CarbonDoser also has a relatively low output PSI which results in an upper limit to how much CO2 you can output and also means you can't use some high PSI diffusers should you desire to in the future. The electronic component also caps the amount of CO2 you can output since the bubbles per second has a limit. I can't say if these limits will actually affect you as it'll depend on the size of tank you have, how heavily it's planted, and how well you dissolve the CO2.
I've actually used both a GLA and CarbonDoser setup.