There are some things to consider, apart from the basics as "good feel" (personal !) , good velocity respons etc.
* aftertouch :
For me (!) aftertouch is a rather essential element of good control from a keyboard.
I still would love to find a 88 key POLY-aftertouch keyboard , which could provide a LOT of additional control !
Unfortunately, poly-aftertouch seems to be gone, apart from the VAX77. Kurzweil had the great MidiBoard, Roland the A80, but a 88 Key poly-aftertouch is history at this moment. I had some expectations for the Rhodes mk7 Midi (for the midi function that is), but now it seems our only hope is that Infinite Response makes a 88 key (weighted) controller someday ...
But even Mono (Channel-) aftertouch seems to be under "pressure" (sorry), since a lot of recent electronic pianos lack this function !!
So pay attention, or look for a real midi masterkeyboard
* half-pedaling aka continuous sustain pedal :
Maybe not as essential for orchestral-only sounds, although I see some opportunies for control here as well, have not had the chance yet to experiment !
In this case, the electronic pianos - in general - have the benefit : recent "decent" models all support half-pedalling (besides the omnipresent sustain on/off function).
Some (!) midi synths / masterkeyboards have this function, but it's lacking in a surprisinly large group ...
Conclusion :
If you don't need 88 keys, put the Infinite Response VAX77 high on your list (great velocity respons, great aftertouch, half-pedaling, additional midi controls).
If you do : you're in for a more difficult search . Make priorities, then check your requirements thoroughly ! Maybe you can find some interesting stuff on the secondhand market ...