SOAS/City >> Essex, purely in terms of reputation.
For SOAS vs City, it depends on your goals; as I understand, City is very reputable in business, so economics may be similarly well perceived. SOAS is fairly well received generally in academia, also it has scope to study a lot of unusual or niche areas both within and outside of economics. SOAS has a higher concentration of international students and mature students as I understand as well, whether this is important to you I don't know
I personally would choose SOAS because I think it has a great deal of interesting options to take, but I realise City would probably edge it out in general terms.