One thing that should be noted, is that it depends somewhat on the grid voltage in your country. In America, where the grid voltage is around 110VAC, your conversion ration is about 1:10. In Europe and in Africa, where we use 230VAC, that ratio is a lot larger, and 24V or even 48V inverters are favoured. Efficiency is usually better for the lower ratios, but as the other answers have noted already, it is only a little better.
The main problem remains the size of your cables. 12V is simply unworkable for anything above about a kilowatt. 24V is good up to about 3 kilowatt, and for anything above that you want 48V.
Cable size isn't the only problem. Parallel battery strings also come with drawbacks, not so much on discharge, but particularly on recharge. If the strings aren't perfectly balanced, one string overcharges while the other(s) is undercharged and dies of sulfation: The worst of both worlds. With a single string, you're limited to maybe 1000Ah. At a C5 rate, that's 200 Ampere, which is around 2.5kw. In other words, high power levels on a 12V system are impossible without parallel strings.
I personally own a 24V Victron Multiplus. I picked 24V for my system as it strikes a good balance between the aforementioned cabling requirements, and the amount of equipment you have to buy. With a 48V system, you have to buy everything in multiples of four. With a 24V system, you buy in multiples of two, which is often much easier on the pocket.
I hope that helps :-)