Hello,
First of all, I would like to apologize beforehand for my English (I am French)
I am soon going to purchase a new instrument, however I do not know too much what to choose.
We recommended me the models 20 of Paxman and 103 of the Alexander

What are the main differences between these two instruments?

Thank you in advance

A French French horn player !

Paxman 20 or Alexander 103?

Many people think the Paxman 20 is more of a tight and focused sound.
Many people think the Alexander 103 is fuller and yet softer sound.

Where will you be playing this instrument? What are your playing plans for the future?

I play in several harmonies with a good level.

At present I play on Yamaha yhr-567 which is good but as I have the opportunity to change, I would like to take advantage of it to take a good French horn,

I think of finding what I am looking for in these two models.

I have played both models in shops and also the Paxman 25. I own a Paxman 25, that tells you where I tend towards. It is even on both sides of the horn and it is amazingly easy to play. The New world bell flare is huge and the addition of a kranz really stabilizes ff playing. If you're playing in Europe I'd go with the Europa or Large flare.