I have the XL and M big green egg and I've owned a keg. My biggest complaints on the eggs are the gaskets are total garbage. Like, laughably awful. I HIGHLY recommend finding a replacement and planning on installing it BEFORE you use the egg. I followed all the recommendations and almost never cook over 550 and mine still fried in the first few months of use. When I asked my dealer why they were so bad he told me if big green egg upgraded the gaskets, they couldn't sell us the replacements. That REALLY pissed me off.
I upgraded the fire grates in both eggs to wire grates and am very happy with that upgrade. The XL didn't really need it (but it still works better with the wire grates) but the Medium definitely did need it. In fact, I'm not exactly sure how anyone does long low and slow sessions with the medium stock grate. Mine easily clogged up on long cooks over about 6 hours. WITH the high-Que, it works very well though.
I also found the Medium nest to be too short and a bit unstable so I had to build a table. I'm not very handy, but I'm happy with my set up now.
The keg, on the other hand, had a different set of issues. It was not air tight out of the box and required some silicone and lots of use (gunk) to get that way. Also, the paint was pretty bad and would come off relatively easy. It was porcelain coated underneath though so no rust issues. I personally really liked the simplicity of the swing grate on the kegs.
The eggs are easier to control the temps...particularly when you need to bring temps down. My keg averaged about 1 degree drop per minute so a 50-75 degree overshoot would take about an hour to come back down. My eggs will come down about that much in about 20 minutes. (This is is under normal conditions and in typical cooking ranges of 250-400.) I'm sure extreme temps would drop much quicker.
2 myths. No matter what you hear, ceramics get CRAZY STUPID HOT ON THE OUTSIDE. Kegs don't. At 400 degrees, my eggs will burn in certain spots and my keg was barely even warm. Also, even my smaller medium egg uses WAY more charcoal than my keg did. Considering an XL egg is roughly the same cooking space as a Weber, I do not find it to be efficient with charcoal at all. I don't think this would matter much to someone who uses their grills once or twice a week, but for those of us who grill every day it adds up. It really irritates me when I hear this repeated over and over again. Yes, it's more efficient than an offset (I assume...never had one) but if you want to save charcoal, get a keg instead of an egg.
Having said that, the XL is a great size. Huge briskets fit really well and there is lots of head room. I'm pretty sure I could get 7 large pork butts on it without having to get "creative."
Don't let anybody talk you out of a Primo because they say pizzas won't cook evenly. Eggs don't either.
The side tables on the kegs serve their purpose but feel cheap. The cast iron grate, however, was awesome if you like that kinda thing and I love the simplicity of the swing rack.
At $200, my Bubba keg was the best grill purchase I've ever made. HUGE BANG for the buck! but now that I've made all the mods (new gaskets, grill table, new fire grate, and the toys from ceramic grill store), my eggs are the best all around cookers I've ever had. They just work well...with the mods.
I liked all the kamados I've owned but I'm not sure I would buy them again at current prices. From a pure cooking standpoint they are great, but I feel like they cost about twice what they are actually worth. Contrary to what a lot of people think, I don't feel like I paid for a "luxury." I think I just overpaid. If I had bought in 10 years ago when the prices were a lot lower, I honestly think I'd have a different opinion.
In closing, they really need to fix those dang gaskets! lol. Hope this helps.