My own experience with NGT's is that they don't mix at all with any of the other Tigers. Ok until they reach about 10 inch and then something appears to change in them like they become teenagers! Smaller than that and they are fine but even when small they're not good with their own kind.
Of course there will be exceptions, this is just my own experience with the three I've had and same with many of the people I know that have kept them.
As for the rest, occasional territorial disputes but nothing more than split fins. My 2000 litre tank currently has 9 Tigers ranging from a 2 inch AT to 20 inch ST and no problems other than one of the big ST's occasionally reminds the rest that it is the boss.
Get a few small ones and grow them on, there will always be a few amongst them that stand out as really good fish.