I don't think this question is only interesting to UK citizens. I am undecided even though I am living outside the UK but in the EU.
The EU plans to spend its 960bn euro budget ( Protected content ) on: 325bn supporting poor regions - The UK won't see much of that since it is not a poor region. 278bn agricultural subsidies - The UK won't see much of that since agriculture is a small part of our economy. 125bn research and training "to boost growth" - I doubt we would get much of this since our growth needs less boosting that other countries. 95bn rural development - The UK won't see much of that since we are not very "rural" any more. 59bn development aid - The UK won't qualify for much of that since we are quite rich. 62bn admin - That is simply an overhead we would no longer have to pay for. 15bn on boarder control - We are an Island a long way from the trouble spots so I doubt this money is coming to us.
Looking at that, it seems that we pay a lot in, 13% of the total, and yet the money is spent on things that aren't priorities for the UK.
People say that we get it all back in trade but I don't believe that France and Germany would stop trading with us if we left, that would be in nobody's interest.