This is Simon's guide to making this decision. It's not definitive but it has the merits of being brief and information light.
1. You can make the egg harder, you can't make it softer. If a harder Brexit means removing ourselves from more of the entanglements we have with the EU then going back when we realise such a removal wasn't the best idea is more difficult.
2. The softest of soft eggs is still a cooked egg. The public voted to leave the EU - to put the egg into the boiling water. So barely cooked at all - the EEA option or similar - is still leaving the EU. And if we want it harder, we can always boil it a little more
So the logic here is to start soft - to step across the line that says "EU membership". This changes little (which is why some Brexit Ultras are opposed) but it has the merits of only ruling out things that are directly related to EU membership such as joining the Euro. Everything else remains available - from the 'semi-detached' situation inherent in being an EEA member through to the hardest of hard scenarios where our trade is determined by WTO rules alone and we have whopping great tariffs on imports (this is a really dumb idea and is why John Redwood shouldn't be allowed anywhere near trade policy).
What depresses me most is the persistence of Remain Absolutists who want to overturn the referendum result because "the people are stupid and lawyers are clever" (I summarise their position here but this is close enough - you can replace lawyers with academics, Guardian writers, bloggers, pundits or blokes who used to work at a bank). It would be rather more helpful if such folk accepted the result - ended the dreadful sophistry about it being 'advisory' - and argued for an initially soft Brexit achieved by stepping across that line.
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