Actually I agree substantially with what M1Ark said although I would not indict any SROs I've met at my current plant. A PWR is a much simpler machine from an instrumentation, ECCS and Emergency Standpoint. The ECCS in a PWR is alomst kindergarten in it's simplicity compared with BWR ECCS. (Look at BWR ADS or RHR Logic if you doubt that!) The EOPs are prioritized for you and heck being in only one EOP at a time simplifies things a lot. Being a BWR SRO requires quite a bit more situational awareness especially in the EOP realm as once you're in one EOP you're in ALL EOPs and it's up to the SRO to Prioritize. In the PWR world so far as I can see, one RO can handle virtually all EOP actions while another RO performs whatever AOPs you need performed. In my experience as a BWR SRO and SM that wasn't possible, at least on a BWR 4 MK 1 plant. There were so many actions to perform simultaneously in the EOP world that you simply couldn't afford to send guys off to perform AOPs. The only exception was performing AOP actions that could directly help you and it best be quick. I will say in the EOP world being a BWR SRO is an order of magnitude tougher than in the PWR world, even in uncomplicated EOP events. That doesn't mean most if not all PWR SROs couldn't become BWR SROs, but if I was an unexperienced Instant starting out I'd go the PWR route.
On the other hand, manuevering a BWR is quite a bit simpler than a PWR. Shutdown Margin is never an issue. Height Dependent Insertion Limits aren't an issue. You don't really have to balance Boron, Rods and Xenon and you can move a BWR darn quickly. Fermi had a very nice feature , with one button you can run back Recirc Pumps to a certain flow which corresponded with around 60% power or so and it happened instantly. Post SCRAM if all rods but one inserted you were ok on SD Margin for all events.
For the most part the only big transitions for me were tripping a turbine on an ATWS (NEVER in a BWR) and the near zero implications of the MSIVs going shut in a PWR post trip. In a BWR you did whatever you could to keep those puppies open.
If I had a choice for an Instant I'd say going the PWR route is easier, practical application on UNCOMPLICATED events is easier, there is much less to put together. Any SRO can tell you instrumentation busses going away is a bear at any type of reactor.
I will agree, BWR SROs and ROs probably have more situational awareness but that's because they have to have it, it's the nature of their world. On the other hand, the average BWR SRO might have a tougher time in the PWR world simply because you have to be carefull in moving the plant. M1Ark was a well above average BWR SRO so I'm not surprised he had no problems.
I will agree, most Instants who don't make it is because of pratical application and Command and Control. If you can't practically apply you'll never be able to do the other. Most Engineering Instants have trouble in that they want to memorize KW ratings and stuff which is really minor trivia, but don't understand what really happens if the pump goes away. An example, I knew an Instant that could tell you how many stages in a Heater Feed Pump, it's power rating and useless info like that. He could explain NPSH, flow vs Head and items like that. BUT if you started the pump he couldn't explain why feedwater pump speeds and flows did what they did. Bring a non degreed NLO into the control room and he'd say, well suction pressure increased to the feedpump, so NPSH went up so... and on and on. This wasn't an isolated case and it's VERY common with Engineering Instants and guys coming out of the Navy. THen if you tripped the boster pump he'd go heywire, look at the wrong things and make hasty decisions.