Uncalledfor sarcasm.
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]I don't know as much about < 4E, but in 5E the stat blocks at completely driven by the ability scores, hp is a function of size and level. It's not like 4E where you could level creatures up or down or had level-based DPR formula determined by whether the attack was single- or multi-target and limited use or not.[/FONT]
Monster design in 4E was way more convoluted a process. The only thing challenging about monster design in 5E is slapping a CR on things and deciding their appropriate number of hit dice (both of which are fairly arbitrary).
uh, are you being serious right now? Monster math in 4th edition was so tight by the MM3 people can and did fit it on a single card. Of all the many faults you could lay at 4th edition's feet,convoluted monster design was in no way one of them. By comparison,numerous people on these forums have posted about discrepancies between the monsters in the MM, and the guidelines for creating them in the DMG. The general consensus as I remember it was that MM monsters in 5th edition were intentionally under-tuned out the gate, but there's still an annoying lack of guidance in regards to special qualities or resistances.
In regards to the OP, I would say go with ToB if you have to choose. If lore is what you're after then it's got more than enough to be usable in that capacity, and in every other aspect it pretty much blows Volo's out of the water. This is doubly true if you're the DM and don't plan on running a campaign with oddball races anytime soon, since you don't lose space to that content. There's way more creatures, with a much wider range of CR, and a lot of the creatures are more-or-less brand new.
That being said if you're truly hungry for options then I would just go with the'both' option as stated by others.