For PVE, in general, neither are widely used anymore. SM/Ruin will have some strengths in 5-mans and 10-mans that no other Spec does, especially in variety of damage sources, but in the end the numbers are just short of many of the other options. SL/SL is quite a terrible Damage source in any PVE situations, and can be used for solo grinds effectively - nothing past.
What SuccySac spec lacks in survivability, longevity and logistics it makes up for very well in pure damage output. In a situation where the Warlock's main source of mana is lifetaps which can be healed off without much a burden (10-mans for instance) this build will be able to surpass SM/Ruin.
Where SM/Ruin can come into decent play is in the fact that it allows a few more options with the remaining points. The ability to snag Dark Pact makes this a very powerful Burn-grind (SBolt SBolt SBolt dead) build with a decent ability to retain mana, while doubling as a first-rate 5-man Lock and a second rate 10/25-man.
It depends here more where you're guild is in progression, here. I will say that this build can be useful in the fact that it gives a good Shadow Damage percent, mid-grade SBolt spam setup, and enough points to round out Malediction (allowing you to take both a SBolt-spam Destro role AND Malediction lock role -- potentially very appealing.) If you already have 2 Malediction Locks, though, then you're still better off Raiding with SuccySac.
SL/SL build is a great survivability build allowing you to wreak havoc on a battlefield of many. While SoulLink is a huge boost to survivability versus low numbers (arena play), the Siphon Life factor is phased out especially in 2v2. This leaves options for a deeper Demonology build, or a shifting of points around within Affliction or Destruction to meet your Arena team's needs.
Siphon life is one of the longest-lasting DoTs a Lock has, which means in places like AV it's entirely possible to have more than 10 people DoTed in the heat of a big confrontation, giving survavabilty to the Lock comparible to no one. Mix in Felpup for Devour Magic and Resistances and you have yourself a BG God. While the damage is comparably slower versus minor targets, enough Siphons stacked allows for 'free' Lifetaps, resulting in a Seed-Spam which quite litterally makes bar-none the BEST Class/Spec combo in the game in large battles.
Real bottom line here is it'll be hard to top out in both PVP and PVE with the same spec, and SM/Ruin and SL/SL definatly arn't your best bet for middle-grounds.
I suggest sticking Affliction-based with 11 in Destruction until you overcome the hit% problem with SpellHit, then your options open up depending on what gear your sitting on (T4/T6 is great Destro, T5 makes surprisingly good Demonology.) This route will allow you to perform in BG (Instant-DoT Spam), Arena (UA/IHoT/CoEx/SBurn), keep up in 5-mans (11 Destro + Dark Pact), assist in 10/25-Mans (Malediction or Doom/11 Destro, Imp), and Drain Tank/Fear Juggle in the downtime.