What is the best system opening, besides London now days in your opinion !?

London is a good solid opening sure! But it's WAY too popular and I think even toddlers now days know how to properly play against it.

I've seen Rey Enigma  (2700+lichess) plays Colle system successfully against IMs and GMs , out of all systems he chose Colle I wonder why? 

What about KIA or Stonewall attack? Or BARCZA SYSTEM perhaps?

If you had to choose just ONE opening system EXCEPT London for rapid play, what would it be and why ? 

https://www.chess.com/forum/view/for-beginners/ten-system-openings

After queens pawn you can play Catalan if declined and basic queens gambit if accepted it is really solid

As black accelerated dragon and kings Indian

KIA / Barcza

For a beginner, the Catalan should be avoided. You are giving up a pawn and you need to learn how to play for the initiative. However, if you play 2.Nf3 and fianchetto your kingside, you could avoid a lot of sidelines in the Catalan which is the recommendation of Keep It Simple. 

As someone who has played over a thousand London System games online, I can assure you that your assumptions about opponent preparation are false. The move order options each sides are a lot more complex than most people realize.

My rating isn't great and my middlegame is weak, but look at my rapid openings as White to see how easy it usually is to outclass people.

I naturally expanded to the Botvinnik System being a Sicilian and English player. 

The value is in having the choice to play an imbalance position.

I wouldn't because no "system" works in all cases.  It would have to be a combination of them:

London - Fails to the Modern Defense

Colle - Fails to anything where the LSB is not blocked in - KID, Grunfeld, Anti-Colle (1.d4 d5 2.Nf3 Nf6 3.e3 Bf5 and now the ONLY move is 4.c4, when after 4...c6, you are in a Slav.  Only after 3...e6 is the Colle playable.

Torre - Fails to 1...d5 or 2...d5.  Works against Nimzo or KID

Trompowsky Attack - Only effective vs 1...Nf6.  2.Bg5, not called the Trompowsky, can also be played against 1...f5, but 1.d4 d5 2.Bg5? f6! and Black is slightly better with best play (See final chapter of Playing the Trompowsky by Pert - computer checked.

Stonewall Attack - Only works against a select few defenses - See Tim Taylor's old book on Bird's Opening, which can transpose to it.

King's Indian Attack - Like the Colle, only effective when the LSB is hemmed in - French, 2...e6-Sicilians

Tony Kosten's old idea from the late 90s of "close your eyes, play 1.c4, 2.g3, 3.Bg2, 4.Nc3 and then look at what Black did.  Fails to 1.c4 e5 2.g3 Nc6 3.Bg2? f5! 4.Nc3 Nf6 and white has nothing.  Instead, White needs to play 3.Nc3! and if 3...f5, then 4.Nf3! Nf6 5.d4! e4 6.Nh4! (Not possible with a B on g2) and the B will go to e2 or d3, once Black plays ...g5, then Ng2 intending h4, and whenever he plays ...gxh4 or ...g4, outpost on f4 for the Knight.

No system works standalone.  I have played the combination of Torre, Colle, and White side of the Slow Slav, 2.e4 against 1...e6 or 1...g6, and the 2.Bg5 Dutch before as White.

If someone twisted my arm and said I HAD to play the same thing every time - Fine!  I play 1.b4!

The London doesn't fail to the Modern defense because you can just play 2. e4 and get an easy advantage.

2.e4 is not the London.

I never said 1.d4 fails.  I said the London fails.  1.d4 g6 2.Bf4? Bg7 3.e3 d6 4.Nf3 and now 4...Nd7 or 4...Nc6 (resulting lines are different, but both slightly better for Black) followed by 5...e5!

And notice above in post 9 I said 2.e4 against 1...g6 - DUH!

The hedgehog system

Excellent analysis from Thriller Fan...

The average club player angling for the London will not transpose into 1d4 g6 2e4. They are more likely to play 2Nf3, 2Bf4, e3, or even 2c3

From a practical OTB POV, the Modern is excellent against most 1d4 players. It can of course transpose into the KID as well, but before that, the unhindered DSB's observation of the e5 in combination with a pawn on d6  pours cold water on the London plodders...

False, people learn to play d4 and e4 on moves 1 and 2 when possible a lot sooner than they learn any openings that have names.

The Modern is terrible because 2 e4 gives a lasting advantage against anyone who's not a patzer.

You obviously don't play much OTB...

You obviously forgot that this conversation taking place on an online chess site.

And online, my observation is borne out here:

https://www.chess.com/tournament/1d4-g6-modern-via-queens-pawn

A couple of my games did involve a double pawn centre, but with the anaemic c3 thrown in.

In any case, I regard online as what sparring is to a real boxing match. 5 to 10% of people che*t.

The Keep It Simple 1 d4 book uses 1 d4 2 Nf3 3 g3 4 Bg2 5 0-0, and then 6 c4 most of the time. The move order avoids a few black defenses.  And it's systematic, no?  But there are exceptions. 6 c4 isn't always played, depending on what black has done. And if black plays a quick ....c5 the move order is derailed. The author covers the exceptions. 

There is no one system opening that is good against everything black plays, white needs to adapt at times. 

The London System is good against everything black plays except for g6, in which case you play e4, which is pretty easy to play.

Isn’t that a Catalan transposed?