I have always liked the 257 Roberts but have been thinking of building a 25 Souper. Any advantage over one to the other or should I just go with the 257 Roberts.

Souper will work a little better in a short action.... allow you to seat longer bullets further out.

I have the reamers for 25-35, 250 Krag Ackley, 250 Sav, 257 Roberts, and 25-06.
I borrowed the reamer for 257 Roberts Ackley and built a couple rifles for myself. One of them was rimmed, and i used 7x57mm rimmed brass.
The cartridges just incrementally change, but the bullets chosen make huge changes. The now obsolete 72 gr Berger and 75 gr Vmax will shoot lots of 1/2" 5 shot groups at 100 yards... but they are not fit for big game and they don't reach way out there.
The 100 gr Hornady interlock make boringly repeatable 1" 5 shot groups at 100 yards, but does not reach way out there.
The 115 gr Nosler Ballistic tip works for me on mule deer between 400 and 500 yards.

What does it all mean?
Do the 257 Roberts [cheap dies everywhere], and focus on what bullet works for you.

I would like a 25 Souper and wish someone would just make it a factory round. Of all the duplicates we have, cant understand why someone hasnt done it yet.

Having no varmint hunting nearby I personally would opt for a 6.5 caliber since my focus is deer and other big game. A Roberts has nostalgia, a 260 or creedmoor has practicality and lots more good bullets for longer ranges, if that is of interest.

A 25 Souper is a 250AI which is a 257 Roberts.

As I have stated before, I love my 25 Souper. The main advantage over the other rounds posted above is the readily available brass. It can be made out of a few different cases.
With the 243 or 260 cases being the best choices.

The advantage goes to whichever makes you smile the most.

That would be one of each LOL

This class of cartridge always seemed to be the ideal platform for a tree stand rifle for deer. Low recoil and plenty of thump. And yes, I would shoot a bear with one ...

As for which flavor, whatever floats your boat. I have a soft spot for the .250 Savage. For no particular reason whatsoever, which is reason enough, right?

I'm a 25 Souper fan. If it has an advantage over the 257 or 257AI in a short action it is that the shorter case, 51mm vs. 57mm, allows you to load heavier/longer bullets without having to seat them as deeply. The 257 Roberts is certainly the less expensive option, as the finish reamers and reloading dies are much more common.

I generally shoot 100 and 110 grain bullets in all of my .257" bore rifles, so COAL in a short action hasn't been an issue, regardless of the cartridge that is used.

Your best bet would be a 25 Super Souper. No reason not to.

I had a 25 Souper Savage 99, 24inch barrel with handloads it more than matched the 25-06 factory loads. Less blast for sure, a sweet cartridge but so is the 250-3000 !!

I shot a 25 Souper for some years, ended up trading it. The next quarter bore I purchased was a Remington 700 VLS chambered in .257 DGR. I enjoyed the cartridge and shot allot of Rochchucks with it in the Great Northwest.

I used .260 Rem cases and when ran through the FL .257 DGR die it necked them down and bumped the should back. I'm entertaining the thought of building a 20" , 9 twist, 25x45 AR.

Though I would certainly like a .25 cal short-action rifle, I see no good or practical reason to, as I have a .260 Rem. 20 years ago I would have done it...today I'd rather spend the rifle $$ on hunts.

The practical difference between the 25 Souper and 260 is 0.07" in bore diameter.

The practical difference is available bullets and BC...

I should have specified "for most hunting applications".

The logical idea would have been the .25 WSM, but that fell flat due, I've read to the patent suit over the base case and also that it was a bit too frisky. A slight shortening, ala 6.5 Creedmore, might take care of the second issue and give a little more leeway with bullet seating depth. The lack of super-slippery .257 bullets and the overlap with existing rounds are other issues. Then there's the fact that, for game .25s are suitable for, the existing choices work just fine.

The boys seem to like their 6.5 SAUMs pretty well. Maybe that case would be a good one to play with.

Ask Rocky Raab what he thought of his.

Jim