In. I've yet to hear a single convincing argument for out. The Kippers will bang on about the 'loss of sovereignty' and how the the UK is more democratic, while simultaneously ignoring the fact that we have an unelected head of state and an unelected second chamber in this country anyway. There's an argument to be made that we don't enough of a say in the EU, but that's in part to do with the fact that a load of the MEPs we have are Kippers and Eurosceptic Tories who don't bother trying to advance anything. I think most people on the out side are mainly motivated by their dislike of immigration, even though there is more immigration from outside the EU than in and the modest economic growth is linked to immigration anyway (GDP has increased with no increase in GDP per capita).
There is no coherent strategy about how the UK would function after leaving that makes any sense. I've heard people advocate the 'Norway model', which is effectively being in the trading zone and accepting the same terms, yet not having any vote whatsoever within the EU as to how things are run. That's worse than we have now. The other alternative I've heard is that the EU will accept us a trading partner without needing to meet any of its regulations to do so, which is utterly deluded. The EU would not accept that because it's both a shit deal for them and also sets a precedent for other countries to do the same, which could bring about its complete dissolution.
There are arguments to be made against trading agreements like TTIP, but the biggest advocates of it within the EU are Tories and there's not a chance in hell they wouldn't sign up to it even if we leave, it would just be under less favourable conditions because we would have a much smaller bargaining position. That actually is my main motivation for voting in, truth be told. While the Tories have a majority in parliament, the EU acts as an effective dampener on their worst excesses. The EU holds its members to far higher standards of employment rights and environmental practices than the Tories ever would. Cameron's recent negotiations were presented in the press mainly about the 'emergency brake' bullshit on in-work benefits (which doesn't make sense and won't work), but very little was written about the arrangements that would mean the UK wouldn't be included in a Europe-wide system of banking regulations. That's the only argument you know the Tories give a fuck about.
The only reason I would vote out would just be to utterly shaft Cameron and while that's very inviting, it's not a good enough reason. For purely selfish reasons I'm also against an exit. I'm leaving the country next year and it would fuck up my plans a little bit, as me and my girlfriend would have to get married first and I'm not a big fan of weddings.