Interestingly, I have owned both but sold the Czech carbine while keeping the 91/59. The M44 stock and fat front sight, aside from the interesting dates and octagonal receiver, make the 91/38 seem chunkier. Indeed, there is evidence that 91/44 is more appropriate, as these carbines may have been updated to post-war m44 condition rather than m38. Either way, it was need, but less-well finished than the 91/59's. More to the point, we don't even know the correct designation for that carbine. We say 91/38, but who knows what the Czechs called it.
The 91/59 is at least kind enough to label itself and so we know what to call it. Interestingly, it is the only Mosin, in general, that is so kind to the user as to tell us what to call it. They are slimmer overall. Admittedly not by much, but their dimensions are sleek enough to feel less clunky. I have owned every type of common Mosin carbine but the only one I retained was the 91/59. The m44's of every flavor were nose-heavy and while the 38 I owned was slim due to the 38 stock, it was not in good shape bore-wise. The Czech was neat and looked interesting and was mysterious, but just couldn't hold my interest as an arm by itself. Hardly more is known about the 91/59's (I imagine they were both updated for exactly the same reason, perhaps we are discussing which type of M-16 updated to m4 status is more interesting, a Vietnam M16 or a 1980's M16A1?), but as a field-carry carbine, it just seems more apt to the task.
Of course, it is merely opinions and I'll rate mine no higher than anyone else. Perhaps I should have kept mine, in lieu of my interest in Czech arms, including a Swiss-made CZ-75. But it just didn't capture my imagination. The 91/59 doesn't either, but it sure looks nicer.