I would counter the argument of post 2 for multiple reasons:
1) System openings do not work as a catch-all system. You actually have to know when they are ok and when they are bad:
Examples:
1.e4 d5 - KIA impossible
1.e4 d6, 1.e4 Nf6, 1.e4 e5 - KIA is a slight advantage for Black
1.e4 e6, 1.e4 c5, 1.e4 c6 - These are really the only cases where the KIA is legit
1.d4 g6 2.Bf4? - This move is bad because of Bg7/d6/Nc6 or d7/e5 - Even Lakdawala, a London guru, acknowledges this!
Colle - 1.d4 d5 2.Nf3 Nf6 3.e3 - ok so far, and after 3...e6, the Colle is fine, but 3...Bf5 or 3...Bg4, all 4th moves by White are bad except 4.c4, which will lead back to Slav theory after 4...c6.
Torre - No good against early d5 - 1.d4 Nf6 2.Nf3 d5 3.Bg5 Ne4! =/+
English as a system - saying "I will play X, Y, Z against everything" is horrible. A popular one is to play 1.c4, 2.g3, 3.Bg2, 4.Nc3 against all. Cannot do that! 1.c4 e5 2.g3 Nc6 3.Bg2? (Even Marin, the king of 2.g3, points out that ...Nc6 should always be answered by Nc3) 3...f5! 4.Nc3 Nf6 and Black has an excellent position as e4 will come with no good place for the White Knight as the Bishop occupies g2. Answer is 1.c4 e5 2.g3 Nc6 3.Nc3! f5 4.Nf3! Nf6 5.d4! And now after 5...e4, 6.Nh4!, looking to entice g5 or harass f5 and g6. If ...g5, then Ng2! and after a timely h4 at a point when Black must take or advance, f4 is a beautiful outpost for the Knight. Despite 2.g3, the Bishop in this line is developed classically, usually to e2.
2) Therefore, scrap everything said in post 2. Here is your answer for effective lines that are fairly simple:
Play 1.e4
Against 1...e5, Slow Italian (Eliminates Two Knights Defense Tricks. 1.e4 e5 2.Nf3 Nf6 3.Bc4 and now 3...Bc5 4.O-O Nf6 5.d3 or 3...Nf6 4.d3 Bc5 5.O-O (two defensive responses by Black, 1 system)
Against 1...c5, Closed Sicilian. It is only equal, but it is simple, which is what you called for. After 2.Nc3, White will play g3/Bg2/d3 and then attack on the Kingside
Against 1...e6, advance variation is simple. 1.e4 e6 2.d4 d5 3.e5 c5 4.c3 Nc6 5.Nf3 Qb6 (5...Bd7 6.Be2! and White will easily be able to castle to safety) 6.a3 Nh6 (6...c4 7.Nbd2 Na5 8.g3 with h4 and Bh3 and O-O coming. White gets a decent kingside attack with a slight advantage) 7.b4 cxd4 8.cxd4 Nh5 9.Bb2! (To cover both d4 and e5) Bd7 (9...Be7 10.Bd3 intending 11.Bxf5) 10.g4! And the Knight must retreat with an unclear game and 3 possible results
Against the Caro-Kann, The Advance with 4.Nf3 (not 4.Nc3) is very simple. An hour of research is all you read need.
I would assume that you prefer those which are easy to absorb and implement. Almost all that fall into this category are what I call system-type openings. The unifying concept is to get a setup of pieces and pawns that is almost universally applicable with the fewest possibilities for the opponent to deviate favorably, thereby limiting the positions you have to study.
d4 systems include:
the london system with Bf4, either with Nc3 or c3
the e3 system, either heading for a colle pawn triangle of c3 d4 e3 or a reversed queen's gambit declined setup with be2 nf3 and 00
catalan type systems with g3, bg2 and c4. quite hard to play though.
i decided not to include the tromp with bg5 and the torre with nf3 nf6 and bg5 because these are not as easy to play in a near-universal manner as the ones above.
e4 systems
the king's indian attack with nf3, g3, bg2 00 and so on. it gives king safety.
the reversed philidor with d3, c3, nf3, qc2, be2, 00, nbd2 and so on. in my opinion difficult to play for someone just starting out as the positions mostly require unusual maneuvering.
c4 systems
the g3 setup, nf3, 00, and could go for a double fianchetto with b3 and bb2 or play it some more standard way with d4 or e4.
the botvinnik triangle with nc3, d3, e4, and mostly g3 and bg2
the reversed tarrasch setup with e3, nf3, nc3 and later d4 aiming for an open game
the original reti concept of double fianchetto, with b3 and bb2, and g3 and bg2, and then d3, nbd2 and rc1-c2, qa1 stuff
that's about it as far as i am aware. i would recommend those that lead to more open tactical type of positions because you need to play them well in any case. and also since i assume you reach more open positions in the scandinavian part of your repertoire. also try to solve tactics everyday for at least 15 minutes.