If you must buy something now, a good psu likely won't be obsolete in the next few months haha. So I'd suggest the Corsair SF450 or SF600 depending on how powerful of a system you intended to build. If you can afford it, I'd suggest the 600W as it gives you room to get more powerful components in the future but will also be more efficient even at low power consumption. The Corsair psu's are easily the best sfx psu's on the market in terms of component quality, warranty, and features for the price. I have read that the Silverstone sfx psu's have had issues with fans being loud, failing, etc. So the corsair is my suggestion.
I really thought the sfx-L units would be better but my research has also concluded that the Corsair SFX PSUs seem to come out on top in terms of build quality.
The noise difference is also similar between the sfx-L units and Corsair's SFX series since the sfx-L units have bearing noise.