Still don't know whether the Original post was intended for PvP or PvE,
In PVE Madness 7/3/31 is very superior to any Deception SPEC IMO, (in terms of just plain DPS.)
If you have a good dps group, VS'ing assassin can be good for burst phases though.
The secret relies in force management, having your dots up As much as possible, not wasting force on reapplying dots too early. DF'ing on CD, mauling on proc and thrashing all the rest of the time, and watching for visual animation/Buff bar for raze proc on melee abilitis. In most raids nowadays there are breaks in combat to regen force that you can go a little bit harder and not worry about draining your force using thrash 4 time in a row with all your dots up and maul not procced yet. But even on the dummy i don't find myself using my basic auto attack assault as a force regen. Being in position for maul is good as well for less time running around as well. And watch your CD on recklessness.
(My thrashes crit approximately 60 percent of the time, they crit for just under 1900 with unearthed knowledge active, GlobCD is 1.5 sconds, and thrash hits twice every time you use it if your acc is at 100%. In short your filler in this spec is a HUGE part of your dps)
PvP however. Deception is way better burst damage IMO. But it is limitted mostly to melee range, with an extra 4 sec stun and a spike slow with reduced Force cloak CD. As a Madness spec sin. you can easily lock down a healer and control what he/she is doing. Insta Whirlwind is amazing now it has 30m range. Madness IMO a little bit more utility however if you spec into reduce Force Speed cooldown. With increased range on force slow, 30M Deathfield, 30M Rooting-dot most melee shouldnt stand a chance against a Madness Sin.
Both DPS specs are advantageous for certain situations in PvP
However after saying that, if you really are the type of player who judges a class based on its ability to 1 v1 others, i think you should have your head checked. Thats not what WZ's or RWZ's are about!