I personally would go with a 426. Camp Chef will limit you to propane and the 428 case is made from a much thinner gauge metal that is very prone to denting. The paint is also crap and rusts very easy....the newer 424, 414, and 428 were just made too cheaply as a result of cost cutting. Specifically on the 426, I would go after the 426D and more specifically I would recommend going with the earlier 426D with the diamond cut outs on the side (see picture #1) below verses the oval cutout (see picture #2). Let me explain why I'm recommending this. First, the 426D is the earliest 426 model that will accept the optional side trays....426A, 426B, and 426C cannot accept these side trays, though they are also fantastic and very stout stoves (see pictures #3 & #4 for the optional trays). IMO these side trays come in handy and are almost a necessity while cooking. They fit right in the case too when you go to pack up. Now why the 426D with the diamond cut outs on the side verses the oval? simple, the early models with the diamond cut out are made with a slightly thicker gauge steel AND more importantly the corners are designed to be much stouter. If you have both 426D models in front of you, it will quickly become clear to you that this is indeed fact. Any of the 426 models can also utilize the Coleman folding aluminum stand...folds down very small and is quite sturdy when holding the stove. the side trays (coleman's offical name is "Chef Trays") are hard-ish to come buy since they don't make them any more and much of the coleman collecting world wants them....they come up from time to time on ebay. if you're lucky you can catch a good deal ($30 or less) if someone doesn't realize what it is they have, but expect to pay somewhere between $50-100 if you really want them and don't want to wait for a deal to pop up.
For running propane on a 426, it would be best to find an older "unregulated" adapter as the newer adapters have regulators in them that are tuned for two burner models and when you run one of them on a 3 burner the BTU will be hampered significantly when running all 3 burners at once...this may be fine if you're looking for a low setting while using all three burners. If you only run two of the burners at a time, you'll be fine. The older unregulated adapters will run a 426 just fine and you can actually get them to throw some pretty big flames and BTUs so you just need to be a little careful. I won't lie, trying to find an older regulator will take some hunting and patience on either ebay, CL or flea market.
As for simmering on white gas, once the generator is heated (a minute or so), you have a full range from an ultra low and very nice simmer on all three burners to nice highs when turned up. On propane, it'll act just like any propane stove and simmer very nicely.
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