Visitor Visa - B2

Hi I am yet to apply for my visa. I'm applying from Accra, Ghana and in 2015 I travelled to Nigeria for a film festival
Earlier this year in August I visited my grandparents in Uk for a period of 30days,later in October I also represented my country in London for a competition with the same Visa for a period of 4 days. My Uk visa is still valid and doesn't expire until February 2017.
My present circumstances is I'm a non-working student in my final year with 8 more months to complete. My biological sister is a US citizen and has sent me all relevant documentation for the application for the purpose of visiting her at her new matrimonial home this Christmas since I missed her wedding in July because of school being in session. in addition my father who is a traditional ruler(chief) is taking full responsibility for my trip between both countries as well as spending money whiles my sister will host me at her matrimonial home whiles I'm in US for a period of 2 weeks during the Christmas at her permanent residence.
Also the company under who's ticket I represented Ghana in October for the competition in London is willing to sponsor my trip to to support our representative for the Miss World competition happening this December in Washington DC. Miss World has sent a letter of invitation. We are applying as a group as other people want to go and support as well. Can I get suggestions on which of these two applications I should apply with and why that will increase my chances of getting the visa. Your suggestions are very much needed. Thanks