Well to answer the question posed by the
OP; it really depends on your partner, your experience and your will to adventure and try new things! Lubrication is a must, as well as clear dialogue between the two parties to prevent any discomfort or...issues. I can point you to an excellent video guide to the topic
ACTUALLY ON TOPIC: Its a hard choice, and depends on your meta. I like the maul. S6, concussive is good, AP4 is ehhh. But it denies anything that isn't a
MEQ. Take nobs- makes them hit last (if they don't have a
PK), wounds them on 2+, you swing first still, ignores any armor they can get (nobs, not
MANz). the maul is good vs non
MEQ's. the sword is...better vs
meqs? lets do some crudemathhammer
sarge, 2A base, 2 weapons (pistol/sword(maul?)) so +1a
3 attacks vs
MEQ
sword: 1.5 hits, 0.75 wounds, 0.75 dead marines
Maul: 1.5 hits, 1.25 wounds, 0.42 dead marines
hmmmmm
vs Ork profile (ie slugga boy)
sword: sword: 1.5 hits, 0.75 wounds, 0.75 dead orks
Maul: 1.5 hits, 1.25 wounds, 1.25 dead orks
double hmmmm
vs Tyranid warrior
sword: sword: 1.5 hits, 0.75 wounds, 0.75 wounds off the warrior
Maul: 1.5 hits, 1.25 wounds, 1.25 wounds off the warrior. If it survives, it strikes at I1
So just off that simple crude math, I reckon (!!does not mean I am 100% correct!!) that the sword will be better vs ANY
meq, and the maul better vs non-
meq.
so now-
DP (codex:
CSM (for 3+ save)) vs sword/maul
Sword- 3 swings, 1.5 hits, 0.5 wounds, 0.33 unsaved wounds (0.25 unsaved wounds with
MoT)
Maul- 3 swings, 1.5 hits, 0.75 wounds, 0.25 unsaved wounds. If from codex

aemons, it would be 0.5 unsaved wounds unless it had Iron Hide, or if its from C

and has
MoT its 0.375 unsaved.
So- the maul is worse vs a daemon prince, unless its from C

and doesn't have iron hide.
vs Trygon
Sword- 3 swings, 1.5 hits, 0.5 wounds, no save allowed.
Maul- 3 swings, 1.5 hits, 0.75 wounds, 0.25 unsaved wounds.
Even against an
MC without an invul the sword still wins via cutting through the armor =\
go the sword