That stuff about being 'targeted' by employers can be a bit misleading. When people talk about being 'targeted' in investment banking they mean firms use university as a way of filtering down their number of applications so if you haven't been to a select list of 5 or 6 institutions they will probably not look at your CV.
Those articles which look at the universities which are most targeted by employers mean which employers go to the careers fairs. In this case Manchester because of its size, will always get more people at the careers fairs, but I wouldn't say that gives Manchester students an advantage when applying. In terms of the financial sector (outside of investment banking) loads of firms will go to careers events in Manchester whereas not many will go to Sussex. This is partly because there are financial firms in Manchester but not many in Brighton, and also because Sussex is a smaller university and has a culture of more left leaning policy types than wannabe financiers, so they get fewer applications from there.
If the posters above are from overseas then I will clear up some misinformation about these cities as I'm from Manchester and I know Brighton quite well. In terms of diversity, they are both fairly diverse cities but Manchester is more multi-racial. However, against that, Brighton is probably about the most 'tolerant' city in the UK, in terms of attitudes towards races, religions, sexuality, it is a very liberal minded place and there is not much hate there. So whilst in Manchester you get more 'communities' eg a big Chinese community, a big Indian community, a big Irish community, in Brighton you get lots of people from different backgrounds who all get on well, it is not seen as odd to be from overseas. In terms of the campus culture, because Manchester is much bigger you get more of those communities of overseas students, there are loads of Chinese/Indian/Gulf States students. Sussex has a lot of overseas students but their market for overseas students is probably more Europe (including the newer EU states) and Latin America.
In terms of the departments, Manchester is much bigger and probably in terms of research they have more research power as they have a lot of staff to cover different topics in Economics, and they have a lot of research centres which cross over into different subjects. Manchester's size is its power, and it is obviously well funded. Sussex is smaller, more specialised and does not have the same financial power with funding. Having said that the department is good for its size, I would say if you are interested in 'global economics', eg trade, development, international economics, then Sussex is a good place. I do regard Manchester as a good department but in recent years their student feedback scores have not been very good in the Economics department and I've heard a few complaints from students that they are not very student focused. On the other hand I know people from Sussex and they like this aspect because its a smaller department with fewer students, the teaching there is good.