In Ixelles, you have 3 very very sought after schools - St André-St Phillipe, St Joseph Boondael and Tenbosch, then a couple more well-regarded ones, many not so well regarded and you really don't stand much of a chance of 1 place, never mind 3 in the most sought after schools. But Etterbeek and Auderghem and WSL and WSP are also not too far from EEB Ixelles school. But if contemplating EEB, I really would get in an application now, even if in the end you do not take up a place, because it's no good choosing to live in Auderghem because of proximity to EEB Ixelles if you in the end get allocated EEB Uccle. EEB Ixelles is the only one of the European schools which is easily accessible by public transport, it's across the road from Delta metro station.
In Uccle, I think you have more good schools, at least that's the impression I get from parents who seem to have less difficulty in securing places than in Ixelles. BUT Uccle is not very well connected to the Schuman area for work and EEB Uccle does not have very good public transport links. You won't get a choice of EEB but if I were given the choice, I'd choose Ixelles for its connections to work, the city centre, nice residential areas.
I know that most children do make it to EEB schools by school buses, but some children have to be at the bus stop at 6.30am in the morning, it is a big consideration when weighing up pros and cons of EEB v local. That is why I am mentioning the public transport options with a short commute to school, or even a short cycle or walk.
I must say that there is a huge Spanish population in WSP, not sure about other communes, I think there is close on around 1000 Spanish nationals in the commune. There are after-school Spanish classes for Spanish speakers in French schools which take place in the premises of a local secondary called Jean 23 on Boulevard de la Woluwe in WSP. There are also Spanish dance classes for children at Centre Crousse also in WSP. I don't think this is a coincidence, probably a reflection of the local population. We have over 20 Spanish speaking children in our children's French chool, the biggest language group after the anglophones.
Personally, I'd search WSL, WSP, Etterbeek, Schaerbeek, Bruxelles 1000 and Auderghem, for convenience to work and also because this area is full of international families and it's rather a nice side of Brussels to live. But that's because I like to be somewhere close to sports, public transport, shops, schools, parks. You might like a more suburban area or more city area.