I use 100% cotton, heavy-weight (300 g/m2, sturdy but flexible) moulded in Europe (in Italy, France, or Germany), chlorine and acid free, pH neutral rag papers, guaranteeing long conservation and inalterability over time.
High-quality cotton-fibre paper is known to last hundreds of years without appreciable fading, discoloration, or deterioration
I love rough texture, but often I use cold-pressed watercolor paper as well, which is moderately textured.
The cotton paper I use almost exclusively is the one of the world-best naturally bright white rag: watermarked Fabriano Artistico, this is internally and externally sized watercolor paper, brilliant white without optical bleaching, with no animal by-products used.
Dating back to 1264, the Fabriano mill’s fine arts papers were used and highly praised by Michelangelo. Nowadays, they are committed to renewable energy and make extensive use of self-generated hydroelectric power.
For graphite and zen ink, I often use Strathmore 500 Series or, especially for collage, Southworth 100% cotton watermarked sheets, or variety of original Japanese and Chinese papers.
In the past, I used French Arches, watermarked, almost exclusively rough.