Without any doubt more is better as has been said but guess we all have to make consessions at times. Cost usually is a big factor. Regarding that I would opt for the 7ch DX7. It's really not that much more money than the 6 but has a lot more to offer. If in the future you find you really do need more channels the DX7 is a very marketable unit.
Jr and Spectrum are the same. One huge factor in my mind over all other radios is their model match and servo sync systems. Especially when flying high cost aircraft don't want to try flying with wrong airplane in TX. The major manufacteres all ma ke very good systems so you have to sort out what suits you.