personally i like asus --really good cooling and great overclocking capabilities--they have just launched a silent version of that card with no fan at all--though its about £30 dearer than their direct cu version if noise is an issue it may be a good choice
I would say that is you are gonna be spending the extra $30 for the Silent version, rather get yourself the 6790, its quicker, and has a higher bit rate, 256bit whereas the 6770 has 128bit. So more throughput, better game play. Just my 5cents worth.
best is a bit subjective i guess--but to me its down to whether they use quality components--how good their support is --how effective their aftermarket cooling is--how well it overclocks and do they still honour the warranty if you over volt to overclock--asus allow voltage increasing
never had an asus graphics card fail on me even though i overclocked them severely
other people will have their preffered maker but those are the reasons i go for asus
Performance wise, the cards should perform identically providing that you are comparing all non-overclocked versions.
The main difference between the manufacturers is usually in support/warranty service. A smaller maker like Sapphire or HIS may not have as good after market support in comparison to the larger makers like ASUS, GIGABYTE and MSI. Take for instance my situation; I live in Australia which is a relatively small market. Therefore a lot of manufacturers don't have warranty service centers here. ASUS however is big enough (mainly due to Laptop sales here) to support a service center locally while other makers I would have to pay expensive shipping to their service center based in Malaysia or Taiwan.
Anyways, I generally prefer to go with ASUS, MSI or GIGABYTE. These companies all use quality solid state capacitors and other hardware on the board, and are overall very well built.
IMO the best in terms of cooling, and service is ASUS. There aftermarket support and warranty is about the best I have ever used and they have the largest amount of service centers internationally. Their DirectCUII cooling design is brilliant too.
Overclocking and Modding I have to vote for MSI simply due to the Afterburner tool. Now Afterburner can be used on other cards but it will always work best on the MSI cards.
GIGABYTE is best for all round value while still offering a brilliant build quality.
Please note that all of these makers use high quality components for the manufacturing.
I have also heard that XFX is very good in terms of warranty with a Lifetime warranty on at least some of their products.