Paterson FX39 or R09 One Shot?

I'm trying to decide which one to purchase. I normally shoot China made films, ie Lucky. I have a brick of Fomapan 400 coming soon so that's what I have to work with for some time. Other than that, I foresee settling on either TriX or HP5 in future for critical work. I do a fair bit of push processing of my film, 400 usually gets rated at EI1600 in low light conditions. Box speed if the light's good. Oh, and when processing my b&w films, I work at 28C. I'd like fine grain and sharpness, a lot of midtones. Wouldn't mind a bit of grain though.

What are the merits of each? Any cons? How are their shelf lives once opened?

Hi Altair (should I call myself Ezio?)
I've actually used them both, and continue to use them both, although with a preference for Rodinal (or whatever you name it). BUT, and it's a big "but" in my opinion, that's because I generally don't mind about a lower-than-box speed.
They're both excellent developers. If you use them with TriX or HP5 expect more than "a bit of grain" though: as stated by others several times, Rodinal -and FX39, which behaves kind of similar- will show whatever grain there is on the film. But, especially with non tabular grain, that results in a very pleasant effect.
The biggest difference between the two might be the development of shadows: Rodinal tends to be a relatively slow developer, i.e. you usually don't get box speed, if you want some discernible detail in zone II and III. On the other hand, FX39 claims -and it really is- to be a compensating developer, so if you plan on pushing films on a regular basis, you might want to opt for the latter.
As analytical geometry would tell you, compensating developers DO compress the midtones, so in that regard Rodinal gives a more gradual tonality.
Rodinal is ETERNAL. I have no direct experience of fx39's shelf life: mine is open since this summer and is appearantly doing fine, anyways.

Hope that helped! Bye.

marco, thank you for your reply, very helpful & informative.

Regarding grain, since Rodinal (or R09) is supposed to be a high acutance developer, that generally means having larger grain. TriX & HP5 is by itself also a bit grainy. But like I said, I kinda like it, so that's no problem for me.

However, since I'm quite new at this, there's a few things that I don't understand. When you say that Rodinal is a slow developer and that it doesn't give you box speed, what does it mean? Does it mean that given the same type of film, the same exposure, the same temperature, dilution etc..will Rodinal need more development than another developer? Would appreciate if you can clarify.

Oh, and in my opinion, altair > ezio

Actually, my expression "slow developer" was improper. What I'm meaning is that Rodinal will -generally- require you to expose your images for a good 2/3 to 1 stop more than indicated, or -otherwise stated- you have to use an EI lower than the ISO indicated on the box -aka box speed-. That's something you can't replace with development time. At least that's what most people's testing point to.
If you're unfamiliar with the concept of altering the exposure index, I suggest you to make a quick search here, you should get PLENTY of useful reading as a result