I tried both dungeons and compared the tomestone gains to Aetherochemical Research Facility.

Castrum: 40 minutes
Prae: 50 minutes
ARF: 25 minutes

Poetic tomes:
normal / roulette bonus / noob bonus
100 / 200 / 100
200 / 200 / 100
150 / - / 100

Poetic tomes per minute:
normal / roulette bonus / noob bonus / roulette and noob bonus
2,5 / 7,5 / 5 / 10
4 / 8 / 6 / 10
6 / - / 10 / -

If a first-timer is with you on the run, then MSQ roulette and ARF are equally efficient and offer the best tome gains. Without a new player MSQ roulette is better than ARF. MSQ dungeons are not worth running for Poetic tomes without the roulette bonus.