Most important factors when choosing primary school...

[fourlittleangels]

That's it really.

What are the most important factors?

For me it would be convenience, reasonable reputation, decent feel upon visiting in person.

Reputation is most nebulous to elaborate on... I'd not want it to be overly deficient in anything, I guess.

For us - important to be able to walk there and for DS to be at school with others from our local community, which left us with a choice of three state schools. Would have a look at OFSTED reports but take them with a pinch of salt - good at box ticking does not necessarily mean good for your particular child. If your child has any particular needs can the school cope with them? What is the "feel" when you go and look round? Are the children happy, is there a good atmosphere, is there plenty going on? Reputation changes at a glacial pace - I've had a few raised eyebrows for sending DS to a school that was under notice to improve about 10 years ago and is now "good". The other school in our area has a great reputation locally but a very poor one within the school communities - also has a "good" OFSTED but is being mentored by teachers from my DSs school to improve their EYFS. I only know that because my DH is now a govenor, but the point is that local reputation can be deceptive.
We found the attitude of the schools varied markedly - where we got a place we were shown round by the headteacher, he knows every child in school by name, he sat down with my DS and chatted and did a little reading and maths with him, there is huge diversity of ability, economic class and ethnicity, but we felt that the school was coping admirably with that and had good strategies for differentiating work. At the "naice" school, we could only look round on a specified new parents evening, we were not able to talk to the headteacher and they were banking on us wanting them because of the aforesaid reputation. The main criticism of their OFSTED was that they fail bright pupils by aiming to get everyone to the same adequate standard. The results at the school we chose are similar even though they have a much lower starting point - they "add more value".
So far (Y1) we've been extremely happy with our decision. DS is loving school, he has friends of every ethnicity and social background, he knows more about other cultures than I do and he is excelling academically. I'm happy that the needs of children with very different abilities and challenges are equally being addresssed.

Being local / within walking distance (I realise this might not always be possible in more remote, rural areas)
The "feel" of the school when you look round.
I'd listen to local views / reputation, but only start taking them too much to heart if tons and tons of parents all mentioned negatives without positives... don't let one person's view skew the whole picture.

@messtins

Excellent post!

It is within walking distance.
When I looked around, the children seemed really proud of their school and enthusiastic about it.
Low staff turnover and a head who is equally respected by pupils, parents and staff.

Perhaps this is only true of our local area, but I have found that there isn't a huge variation between primary schools. They are all of a similar standard and all have a similar 'feel'. However, the secondary schools around here vary hugely.