special abt 780i is you can install 3 identical graphic card making it tri sli at full bandwidth triple at x16 mode
and 790i also does the same thing but here you will have to install dd3 rams and wont support ddr2 rams.even performance varies too.
again you have not mentioned your budget anyways brands to opt for abit,asus and gigabyte.if you are looking for cheap go for asrock