The way I view the key issues is the following. Underneath I've put whether on each issue I think EU, EFTA or Leave.

Single Market
The UK's largest trading partners are the rest of the EU, but the EU is stagnating and shrinking as both a share of the global economy and a share of our trade. Exports to the EU is 45% of our total trade. The UK runs a massive trade deficit (over £60bn per year) with the EU and oddly enough runs a trade surplus with the rest of the world so the Leave side argue that the EU would definitely sign a Free Trade agreement with us even if we aren't in the Single Market itself.
I think we should stay in the Single Market but it's far from the only thing we are or should be doing. So EU or EFTA. I'm only 95% not 100% confident the EU would give a Free Trade agreement with us without being in the Single Market even though it would be definitely in their interests to allow it as it would require the agreement of all nations in the EU and some may choose to be spiteful.

Migration
The EU (and the EFTA/EEA) allows free movement to live, settle, work or retire anywhere in Europe (and vice-versa). The equivalent IMO of the USA signing freedom of movement with Mexico and Central America. I'm pro-free movement but it's an unpopular opinion.
I like this so EU or EFTA, but others who hate it would make sense to go for Leave.

Customs Union
I only recently learnt that despite being in the Single Market, the EFTA nations are not in the Customs Union. So inside the EU the UK has the same customs rates as the rest of the EU but in the EFTA (or a full Leave) we could negotiate our own trade deals and would sit independently on bodies like the WTO. The argument to stay in the EU is that we can negotiate better trade deals with counties like USA and China if we go toe-to-toe as part of the world's largest trade organisation. The argument for EFTA is that the EU doesn't just care about our interests anyway and we are the world's fifth largest economy so could negotiate good deals in our own right without waiting for the lowest common denominator for countries like France. Switzerland has a free trade deal with China which the UK as part of the EU does not, it had a free trade deal with Canada before the EU.
I'm leaning EFTA on this one, I think we could negotiate deals quicker and easier if we don't need to appeal to French farmers.

Influence on Single Market laws
The UK gets more say on Single Market laws in the EU than in the EFTA so this would be an argument for Remaining. Though Hazir has tried to spend the last 15 years saying the UK has no influence anyway so it would not be if he's right.
Remain in the EU

Influence on the Global Stage
Do we have more say in the EU or not?
Frankly I don't think it matters one single jot. We're the world's fifth largest economy, fifth largest military, permanent UN Security Council member. Our international relations are frequently more aligned with the USA than France or Germany. I think this is utterly irrelevant. EU, EFTA or Leave it's irrelevant.

Democratic accountability
The EU applies a lot of laws that I think should have nothing to do with it, like on Social matters etc. EFTA nations are only required to apply about 5% of EU laws and those are typically on things like standards that are typically globalised anyway. EG electronics products are CE certified in the EU, but almost anything you buy is certified both FCC (USA Certification) and CE anyway. This would be the same whether we stay or Leave.
EFTA or Leave

Contributions to the EU
The UK contributes £13bn per annum net of rebate to the EU which is rising as we are growing faster than the rest of the EU and get effectively charged more the more we grow. In the EFTA this would come down to about a third of the figure.
EFTA or Leave would reduce or eliminate this.

Employees Rights etc
(See Democratic Accountability)
Some Trade Unions* are campaigning to remain because of this. The EU dictates on social policy a lot of restrictions as to how much employee rights there are. I oppose this, I think it's got squat to do with the EU and should be decided locally. If one nation wants to be socialist it shouldn't apply to us. I trust the British voters to decide on this. I don't think this applies to EFTA nations.
EFTA or Leave.

* Some are campaigning to Leave due to high migration suppressing wages in their view.

Security
It's being argued by some that the EU improves security due to us trading information with other nations. Others argue it hurts security due to unrestricted migration.
I think this is irrelevant. The main nation we trade info with is the USA which isn't even part of the EU.

Common Agricultural Policy/Fisheries Policy
Gives a lot of subsidies to farmers and requires a lot of tariffs on non-European food so means that food costs customers a lot more than it would otherwise. Also hurts Africa because they can't export agriculture to the EU without high tariffs. Doesn't apply to EFTA. The UK has wanted the CAP/CFP reformed ever since we joined, it never has been and likely never will be.
Definitely EFTA or Leave this one.

Summary
I think that covers the main issues, though I wouldn't weight each equally personally (in fact I view two to be complete red herrings). I would rule out Leave to mean Leave completely, I think we should be part of the Single Market. So to me it comes down to the EU versus the EFTA which has been very little discussed here.

EDIT: Just counted my issues break downs and I see the following (though I don't weigh each equally as I said), discounting completely both the ones I said were irrelevant.
EU: 3 (but the most important 3)
EFTA: 7 (everything bar influence in shaping Single Market laws)
Leave: 4