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I just keep going round in circles, I make a decision and then change my mind again. I know no-one can make the decision but me but does anyone have any final words of wisdom.
You're confusing yourself by throwing too much into the mix and forcing yourself into compromises.
The Tamron is optically not that far from the Canon, but the focus speed suffers (what's that worth to you?)
A cheap 50mm 1.8 is optically superior to either of those at f2
It's actually probably better at 50mm at all the large apertures (although no use at the other focal lengths
).
You won't be using the 50mm all the time, but it'll be great for the occasions it suits your needs
You don't always want all your shots to be full baby shots (the pictures will be boring) Have a look through some pro sites of baby pictures - it's that kind of variety you want and it might be that the 50mm becomes too short for capturing some details.
On the occasions you're not shooting with lights and a background - bokeh will help to 'clean up' the background (it can't work miracles - but used carefully it's great)
And Yes; for what it costs the nifty is a no brainer, but as with all things in life getting a 'good' picture out of it still requires you to work.
Buy the Tamron zoom, the Sigma 30mm, 1.4 the nifty 50 and explore the light.