I struggled with this question hugely for my Dd. This school seem good at this and that school seem better at that, they are all no good at the other thing and how do you know how it will actually work out in reality, all you hear now are promises and advertising talk, league tables show they are both no good for DC with low prior attainment.
I visited a couple of dozen of schools, including Special Schools and settled on my choice very late in the year actually.. Ultimately it is important to focus on factors and criteria that are really important for your DS, his specific needs and circumstances. It will also reflect your values and priorities because you can't be sure, it is a leap of faith..
I wouldn't discount school number 1 yet, OP.
You need to make your list of key factors and criteria that are key for you, for your DS circumstances, and visit, visit, visit (several times, open day, group tour, 1:1 arranged visit by appointment, with DS and without), observe (the classes, the children, the teachers, everything), talk to the teachers and to the Senco (and deputies as Senco will be rarely involved with your DS), to managers. Senco can promise a lot, but teachers actually teach and managers decide how to organise and spend money IYSWIM, and the deputy is the one who does it. You need to observe and talk to all of them to figure out how the SEN actually works at the school.
Of course you don't want DC to go to a school that does not understand / provide for their needs properly and fobbs you off with teflon statements. However cosy departments can also be a trap of low expectations and abandonment where they don't do enough educationally, their could also be sink sets... A few factors to consider:
Long term: you don't seem keen on academic extra support, but does it mean you don't want/expect your DS to achieve GCSE? What do you hope for him for his future after school? Is the school geared to prepare him for that future?
Competence: the school with better results, more advantaged catchment area might have more resources, fewer problems, better teachers/Sencos/managers, have better ability to manage and organise and deliver what your DS needs, provided they care, want to, have the right culture. Look in league tables at Progress8 measure and their results for prior low attainers and disadvantaged pupils. It will show whether they do well for all students or only advantaged top sets (that would do well anyway), talk to them about targets, do they stretch all pupils, do they abandon difficult pupils (like in the TV program they decided to help low hanging fruit kids and left behind many others). My expectation, this leaving behind will be more likely in a weaker school actually, the stronger school is geared up for higher Progress8. Beware of sink sets for all SEN and underachievers combined that don't help anyone.
Dynamic: the school with poor results/ difficult catchment is likely to have more problems, which are likely to increase and escalate as they would struggle to improve, keep up, parents would vote with their feet, there could be difficulty attracting and retaining teachers, budget... Ultimately with best intentions they might struggle to deliver and leave DC with SEN with very little to show for... Beware of sink sets as well.
Ultimately, after properly visiting the schools, your instinct will tell you.