A few weeks ago while sketching outdoor, I had to borrow a watercolour brush from my friend because I forgot to bring mine. He lent me an Escoda Optimo travel brush. I used it and was surprised by how soft the brush was, and yet it's still firm and responsive enough. My usual brush is the Da Vinci Maestro series 1503. Da Vinci Maestro is a firmer than the Optimo so I could really feel the difference straightaway.
In terms of ranking, Reserva is top of the line, followed by Optimo and then Versatil. They are all quite capable of tapering to sharp points. However, after application, only the Reserva and Optimo would taper back to the sharp point.
According to Escoda, the Reserva series use only male Kolinsky-Tajmyr sable hair. And this hair comes from the Tajmyr region in very northern Siberia. It's noted for its ability to hold a sharp point. The male hair is stronger and so has a better snap and is also slightly firmer than the Optimo.
Their Optimo series of watercolour brushes are made from Kolinsky sable hair. And used in manufacturing are from both male and female hairs. Optimo brushes are noted for their softness and natural spring. They are excellent for watercolour, but can also be used for acrylic and oil painting.
Both Reserva and Optimo are wonderful sable brushes that have large water capacity. If I were to do a blind test for softness of these two brushes, I would not be able to tell them apart.
The Versatil series is a synthetic brush developed as an alternative to the Kolinsky sable. It's firmer and performs somewhere between synthetic brushes (like those white bristles) and the sable.
All these three series of brushes are available in the traditional wood body as well as travel pocket versions.
In terms of price, Reserva is slightly more expensive than Optimo, and both of those are much more expensive than the Versatil.
Below are some tests I did with the Optimo, Reserva and Versatil brushes.
Here are the brushes grouped by size. The Versatil actually has thicker bristles. The sable bristles are very fine. You can also notice that the sable brushes have a bit of belly as compared to the Versatil which is mostly straight. Those hair characteristics really improve the water capacity of the sable when compared to synthetic brushes.
These are size 6 brushes. At smaller sizes, the Reserva brush seems sharper. And at smaller sizes, the sable brushes hold more water than the Versatil.
These are size 8. For some reason, the Optimo brush seems to be more able to get finer lines. All the brushes are made manually so there will be some difference in quality even within the same series of brushes.
Note that with the circular motion, the Versatil brush wasn't able hold its bristles together resulting in more lines rather than a single strokes. Reserva and Optimo are excellent at holding the bristles together to maintain a sharp single stroke.
These are size 10. Same applies as size 8 except the strokes are thicker.
Escoda makes wonderful sable brushes. Reserva and Optimo are their finest watercolour brushes.
For more detail work, especially those that require thin strokes or fine details, I recommend the Reserva. I perfer the Reserva for my pen and ink and watercolour sketches because they are easier to use when keeping the colours within the lines. If you don't require that kind of precision, then the Optimo will suffice. Price difference for smaller brushes aren't that much and I would still recommend the Reserva if you want to get a good sable brush. These brushes last a long time if you take proper care of them so it's still worth the high price they command.
You can find these brushes at Jackson's Art Supplies (UK) (free global shipping for brush orders above £20).
They are also available on Amazon. Here are direct links:
Search Utrecht Art Supplies (USA) too.