The problem with comparing Pratten (style) flutes to Rudall styles is that the Pratten was/is a specific model style (large hole, large bore, generally if not always a one-piece middle section with all 6 holes in it), but the Rudall, Rudall-Rose flutes vary greatly, as those original makers made a variety of flutes. Some are smallish-holed, some not, some are single mid-piece, though most are not. Some are quite loud, easily holding their own against a Pratten, and others, well, not.
In general, the Rudall, the originals and the very various modern copies, are daintier to hold, with a split between the right and left hand, which may or may not be important to your playing style. More tenons, like more keys, of course, can cause more problems, and so the lower maintainance and most air efficient is the Pratten. But that’s not necessarily always true, either.
Both original models were designs created for contemporary (at the time) classical music, with ideas to improve volume and/or intonation. Modern Pratten types (unlike the originals of both styles) are general made for Irish music specifically; louder, throatier, etc., great session instruments, though they are not limited to that music and well-made Pratten types can be played softly and sweetly as well. Prattens tend to have better intonation, particularly in the low end. Modern Rudall types are great for Irish music as well, of course, but they were made more in the tradition of earlier classical flutes, especially the smaller-holed models, and the difference in playing ease and sound is simply a matter of opinion, hand size and what you get used to.
Ultimately, the sounds from both – and this in not meant as a patronizing, well-trod sentiment, but a fact – comes from the player, and both styles are capable of whatever the player can put into it. So, ultimately, if you’re deciding one over the other, it’s is much, much more important to find which feels better in your hands than which is said to produce a certain sound. Chances are, you will only produce whatever sound you already produce until you grow, and then you will still produce that new sound on either style flute.
Great players will switch makers and flute types, Pratten or Rudall style, and most of us will never really hear a difference. It becomes more a matter for the player, who simply felt that, for whatever reason, they like playing a particular flute or a particular design.
Lastly, since you are not really talking about the original makers, I take it, but the modern versions, the differences between makers is far more varied than whether they based their models on a Pratten or a Rudall.