When I began bashing out mortices about 25 years ago, this was with firmer chisels. They were thick blades and 30 degree bevels. They were hard work - limited penetration of the wood, and hard to pry the waste away.
Three Woodcock firmers on the left ..
I heard about Oval Bolstered Mortice Chisels (aka pigstickers) and bought a few vintage chisels. The early ones were discarded and eventually replaced with long blades. As Jacob reminded us, the tapered sides aid in preventing these blades getting stuck in the mortice. Wonderful chisels and a clear step up from the firmers.
The journey continued when Ray Iles brought out their version in D2 steel. There is a lot of hype about how this steel lasts forever. Well, it is true that they last much longer than the laminated steel of the vintage Wards I have, however this is only really relevant if you are working very hard and abrasive woods. The Wards (among others I have) do a great job and will last through several mortices before one needs to rehone. The RI just last longer. More relevantly, they are beautifully made, and the blades are long. The problem these days is finding good quality vintage mortice chisels.
Here is a 1/4" RI flanked by a couple of Wards ...
So several more years go by and about a year or so ago I began testing blades for Lee Valley, and then testing handles as well. Their mortice chisels have the size and heft of an oval bolstered type along with the appearance of a sash mortice chisel. I cannot really comment about the handles, since the ones I have are pre-production and larger than the production (they are fine for my large mitts but I recommended that they be made smaller for the production version). The blades, however, warrant a closer look. They are superior to the vintage and RI versions. Like the others, they have trapezoid sides. The steel is either A2 or PM-V11. Frankly, I chopped metres and metres of mortices, and my arms gave out before the A2 steel did. The PM-V11 would last even longer. As I pointed out earlier, the laminated vintage steel did the job ("good enough"). The A2 (which is also what LN use) is better. The PM is better still, but is it necessary? Still, that is not the best thing about these blades. They are fuller/deeper at the pointy end, and this creates more control (this is the important point) and better leverage .... I do not lever much, but eventually one does need to lever, and then they are better at this.
RI, Ward, Veritas ...
The gap between the vintage OBM chisels and the Veritas is not huge. If looking to save bucks, find a couple of vintage chisels. If you have the bucks to spend, either the RI or Veritas will make you happy, the Veritas a little more so .. but only if used them side-by-side. I think good/bad chopping technique could make a greater difference than the physical side of these chisels.
Regards from Perth
Derek