The last post by Inn2 was so obvious (when you see it) yet so brilliant!

I have played 1.e4 all my chess career (13 Years).  Recently I had been thinking of switching to 1.d4 but couldn't really make up my mind - it seemed like a lot of work.

Then after reading Inn2's idea of deciding which you would rather face the Nimzo or Siciilain, QGD or the Spanish etc it all became obvious!

To quote Inn2 "for me 1. d4 is a no-brainer choice"

Thanks Inn2

MNb: Yes, Najdorf and Sveshnikov are very difficult. Well, I'd probably go 3.Lb5 in the sicilian. (I succesfully tried 2.c3 in CC.) Maybe I try 3.d4 vs 2...e6. I'd probably play 3.Nf3 avoiding the Nimzo.

One of my concerns are the solid lines (QGD, Petroff, Berlin). I'm not really used to long theoretical drawish lines.

It's difficult to say anything general about the sicilian. It's not one opening. The Nimzo is a very hard nut to crack. It would be very nice to get something like 4.a3 or 4.f3 to work.

QGD: I've followed the development of the Bf4-line. Still, advantages are often very small as they seem to be in the Bg5 main lines.

Semi Slav: Also difficult. I tried the Meran in CC with one nice win and a horrible loss.

When considering picking up 1.e4 you should aks yourself two questions first:
1. What to do against the Svesjnikov?
2. What to do against the Petrov?

The third question must be:
3. What to do against the Najdorf?

These Black defences are at the moment the hardest to crack.

I do not know what you played against the Symmetrical English, but in case you choose 1.d4 I want to mention the transposition 1.d4 Nf6 2.c4 c5 3.Nf3 or 1.d4 Nf6 2.c4 e6 3.Nc3 c5 4.Nf3, so you might already have something against the Benoni.

I'm currently playing 1.c4 in OTB chess (using Kosten's book). I'm thinking about switching to 1.e4 or 1.d4 instead. Which should I choose?

Perhaps it would help if I've list what I've played over the years.

Black against 1.e4
OTB: Alekhine, Sveshnikov, Caro Kann (briefly), Alekhine.
CC: French, Sveshnikov

I don't trust the Alekhine completely but I like the dynamic positions that often arise. I'm thinking of taking up Najdorf in CC games using the recent book by Arizmendo & Moreno.

Black against 1.d4
OTB: Stonewall, Vulture, Stonewall, Slav, Leningrad Dutch.
CC: Leningrad Dutch.

I have good results in the Leningrad Dutch. I might try the KID in forthcoming games (using Gallagher's recent book.)

White:
OTB: Larsen, e4 and English
CC: Nf3 (like Kramnik), English and e4.

So, I've never really played the Ruy Lopez or Queen's gambit. In OTB chess I played the King's gambit and in a recent CC game I tried the Scotch.