I am looking for good weather textures and weather engine. Though about REX 4 and Opus?  I also heard that AS has a good weather engine. Any ideas?

ASN amazing weather engine, and I use Rex 4 for textures and they are awesome. 

Highly recommend REX 4. Easy to use & the installation of the textures take no more than 5 seconds.

REX4-Direct, gamechanger for me, and still using FSX...

+me ASN is great. REX4 is fantastic. It is super easy to use and it is just textures. I just got it and for me the jury is still out of the cloud textures. They are great. I am just not sure that REX 3 Clouds where not more realistic. Had REX3 for over 3 years but REX 4 for only a few days so the jury is still out on that one.

REX Texture Direct is great, many variations of textures for several things such as clouds and sky. 

I will say the most awesome thing I noticed after using Rex 4 was when there was overcast skies you could not see the ground through the clouds. Total cloud coverage which was just amazing and you could see the different cloud layers. It was truly an amazing sight. 

I like PILOTS R world Weather