Hi

This is such a difficult Question as has been said much depends on you reasons for
Wanting it.

If you buy a full keyboard with on board voices you can use this as a midi module for BIAB all keyboards of this type will have a set of basic GM midi voices + a whole other host of panel and extended voice banks however to access the later in BIAB you will need a PAT file or a Sona instrument def file to convert..
This way you get a sound module and a keyboard.
Have a look at the YAMAHA DGX range these have a full set of XGlite Voices and a full size 88 note piano

Personally I have a YAMAHA CVP 405 in polished mahogany but it’s the size of a baby Grand piano BIAB is great played through this using its voices and using the full key bed for playing.

But for every day use I use a NOVATION IMPULSE 61 Controller keyboard via an AKAI IEpro interface to my laptop then use various VSI /DXI etc in BIAB
Just some thoughts
Mike

BIAB2021 UltraPlus,AsusN55S1Tbssd, W10/64,Akai EIEpro
Yamaha CVP405,SquireStrat, CoolsoftVMidSynth
Novatation Impulse61 Ctr kbd, Cwalk blab Kontakt

http://mikesmusic.byethost16.com/