I've only ever had one creature follower, and it was a Steadfast Dwarven Sphere called Mr. Rollaround. Stupid Esbern hit him with fireballs and then killed him. -.-
Anyway, I personally cannot stand Rieklings, so I would definitely pick a sphere - or even a spider - over one. Mr. Rollaround was way cool, not least because he only ever hissed (and clanked). I don't know if a Riekling follower would speak (in their language or English), but if Rieklings in general are anything to go by... yeah. No thanks.
I'm assuming an NPC can do everything a Riekling can, and then some.