I want to buy some altcoins due this big dip and strenght my long term position with several coins...
I'm going to strength my position in:
-NEO
-TRX
-EOS
and, perhaps in ETH
What do you think... is there any other altcoin that could be the next surprise after this present dip?
Definitely ETH. The other three definitely had a lot of hype, which pushed the price too high - not saying they're bad, just that hyped coins can be overpriced.
I would expect ETH to bounce back stronger than the others you've listed, but it can be sensible sometimes to go with more than one coin.
I would say put the largest share in ETH, and then a bit less in each that you think looks good value.