I am learning the QGA (Queen's Gambit Accepted)

After 3…e5 black is OK after both e4 and Nc3.

Nf3 attacks e5, defends d4 and does not commit White to following into the Orthodox Variations. It allows for him to keep the option open for the Slav defense and the Semi-Slav as well. It also makes the idea of an early Bb4 move less palatable. Of course, those are QGD lines. In the QGA, White can play also 3. e3 with an interesting Rook trap line, play e4 with some sharp lines also or 3. Qa4+ to immediately go for the Gambit pawn. 3. Nc3 let's Black also play for regular development rather than try to hold the extra pawn, which he cannot do without some help from White, e.g. 3. Nc3. There is a study that's over 300 years old that proves that if White sets up with a later b3 advance, Black has a worse position as the Queen will grab at b3 and now b5, c6 and b7 are weak with little to no development on Black's part.

All three moves are perfectly playable... Nf3, Nc3 or e4.

Nf3 is the most popular move, partly because it limits Black's options by preventing an immediate e5 move, and partly because it is fashionable.

Chess Grandmasters are as fashion-conscious as teenage girls.

1.d4, d5 2.c4,dxc4 3.Nc3,Nc6 also allows black to transpose to a variation of the Chigorin.

White may wish to stay in calmer waters compared to something highly tactical like the Chigorin.

That's why I always say memorize openings to play well at a particular opening. 3. Nf3 3. Nc3 and 3. e4 are the main variations of the QG Accepted. I won't be chess.com 2000 now if I did not memorize. Memorize and play it. I improved that way. Tactics tactics tactics is a hoax.

I just play e3.

3. e3 is one of my favorite replies to the QGA because at my level, there are so many people who try to hold that pawn.

Again, perfectly playable.