What level are ya?
Affliction is the *fastest* way to level, although it sort of comes with a price. Where Demo is very quick at single targets (and very powerful, might I add), affliction excells only when taking on multiple targets, allowing overall DPS to stack up from multiple sets of DoTs on multiple monsters.
Having tried a few different specs all over the board, I can tell you that with a steady flow, a much higher amount of concentration, and more will power you can level a good deal faster with Affliction instead of Demo. Demo is also able to handle multiples, but not with quite as much power, and is dependant on the pet for ALOT (too much I feel.)
As for your builds, your first Affliction buildset is pretty well put together. Again it depends on your level, but there are some things to watch out for as certain talents start out good, then get pointless and then may be worth it again later.
The first is Drain Soul, which is a good choice at early levels due to the Mana gain, but later becomes stupid. It remains relatively pointless (I believe it's broken, whatever the case it does not usually return the mana it promises) until you again can make good use of it due to it's agro reduction in later groups/raids.
Empowered corruption is an amazing talent... when you're high enough level to have a ton of +spell and +shadow. The increase from Empowered corruption is actually relatively miniscule until that point, as it is simply a modifier on your effective +spell while casting Corruption - that's it. I would say the talent is underpowered until at least 65, although I'm not doing any math on that badboy. While Improved Agony is often looked down upon (and for many good reasons) it remains a decent choice for straight grind situations until you have that +spell to make Emp Corruption worth it.
Demonic Embrace is far superior to Improved Imp in levels 10-50, however some may argue the additional 11.4 STA to everyone in the group at lvl50 and 20 STA to everyone in the group at lvl62 is better than the 15% increase in your personal STA. This, again, gets straight shot out the window once you start getting good STA gear from OL and PVP. Rule at 50 is if you have 400sta or more then Embrace is better, Rule at 62 is 667sta or better then Embrace is better.
If you're gonna go deep into Demo for grinding I suggest getting 3/3 Manafeed for the trip up, however 90% of people contend that once they get decently geared 1/3 is enough, in which case a respec would be in order so you could fit those 2 other points elsewhere. As for me, when I specced Demo I kept 3/3 because I HATE when my pet gets LoM, and certain BG and Arena situations call for as much mana as possible - including for pets that arn't your Felguard...
As for the Master Summoner thing, it is a passive effect that actually stacks with Fel Domination. You are right, however, in the fact that if you're grinding/farming both talents are somewhat of a waste. One solid arguement is that after a run of 5-15 monsters, it can be quicker to simply summon a new Felly, and with these talents that is not only by far true, but also has a reduced casting cost. Another prime use of the talents is that SL/SL will use it to pop VW Bubble on themselves, cause a fuss somehow (generally Deathcoil) and then quicksummon a new VW to resume the SoulLink. It's a solid tactic but not good for what your looking at right now.
For a straight-shot cut to the bone Felguard build that will work well for a while, use
this, and while you definatly can use it immediately at 50, most suggest either getting enough levels to put some points into Destruction or Affliction before actually making the change.
Improved Slave demon is pointless. If you wanna go SB Spam with Felly, then also make sure to grab Demonic Tactics.