As Teya and I packed up for the 2023 Guardian Conference we had the luxury and burden of selecting which pistols we'd be training with. Over the years, with training at ITTS, Front Sight (now Prarie Fire), CENTER-T, Thunder Ranch, VerTac, and Sentinel Concepts we've tried a few approaches that might help you select what you train with depending on your personal training goals.
I understand that not everyone has the option to select one pistol over another for training, I've been there too. That's ok, and has some advantages, but in my thought processes below you may find benefits to picking up a second pistol of similar design. Here are some potential paths and outcomes.
Focus on Your Carry Gun: The ultimate in training effectiveness. Taking your carry gun to a training course is a great way to learn the gun and find its strengths and weaknesses. Do it with your carry holster and you'll get good with your draw too. I've done this at Front Sight and believe it significantly improved my competency not only with my carry pistol, but also with my ability to adapt as I had many a draws and shots that were not perfect. The downfall for this is that chances are your carry gun was chosen for it's size and weight. As a result smaller carry guns tend to be harder to control and have lower capacity. Reload training is great, but loading magazines over and over can get old. Higher-capacity magazines can offer more grip and fewer reloads, but also defeat some of the value of training with your carry gun if it means changing the grip size. Fatigue from a single range session is one thing, fatigue from multiple full days of training is completely different.
Focus on Learning the Course: If you feel competent with your carry gun and would like to push your performance and focus on what's being taught at the course, then bring either a pistol you know well, or something larger than your carry gun. Longer slides mean softer recoil (in general), and a longer grip means better handling and higher capcity. This option should keep pistol frustrations out of your mind and let you focus on what is being taught and learning techniques.
Focus on Learning a Gun/Platform: If you'd like to learn a new pistol or style of pistol and are confident in your general shooting skills, take something new to the course. This can be the most difficult if it happens to also be a new course. For example I took the same Front Sight 4-day Handgun course several times and each time brought a different gun (Glock 19, Glock 34, Springfield XDm, Walther P99AS, Grand Power K100). If you're already familiar with the course, running a new or different gun will really show you how you perform differently with that gun, or how that gun's unique characteristics make a certain drill easier or tougher.
The Size Factor: This time both Teya and I are taking larger-format versions of our carry guns. The advantage with this is it's sort of a combination of all three angles mentioned above. As mentioned, larger guns generally shoot softer and offer superior handling as well as increased magazine capacity; enabling you to stress less over the pistol and focus more on the course material. If you construct the right pairing, a larger variant will let you learn the platform and the course so you can work on skills at home with your smaller gun in shorter sessions. This is especially relevant with today's "micro compacts" that are fine for shorter shooting sessions, but not necessarily much fun for a full day or three of shooting.
Graham's Picks: BUL Armory SAS II Tac as primary and BUL Armory SAS II UL as a backup. This time I'm bringing something different, looking to learn both from the course and the firearm. I've been carrying the SAS II UL as a summer gun and the SAS II TAC offers a little more capacity and a slightly softer-shooting experience. I have attended a course before with a 1911 (ITTS Intermediate Handgun with a GI 1911), but that was literally decades ago and with a gun that handled completely differently.
Teya's Picks: Canik METE SF (with Shield RMSC) as primary and Canik METE SFT as a backup. These are laarger versions of her carry MC9 and will offer a more comfortable shooting experience as well as higher capacity. Teya has used Caniks at CENTER-T (TP9 Elite Combat), Thunder Ranch (METE SFX), and VerTac (METE SFT). The move to the compact METE SF is as compact as the line gets without going micro.
What Have You Run? I'm curious to hear form you how you've selected your training pistol and if you've considered the approchaes mentioned here. If you haven't been to training yet I hope this helps you make a wise decision to help you get the most out of your training. It's not an inexpensive endeavor, but neither is defensive use of a firearm.