It really depends what your after and long term goals. Depending where you buy the $800k one might get you into a better location.
However the 3x $270k properties would probably get you better yields, lower risk as you have diversification and 3 assets going up in value as apposed to one.
On the other hand 3x $270k properties while the cashflow may be good you could be compromising on location or quality of asset and hence capital growth.
If it was up to me, I would say 2x $400k properties followed by $800k.