Safe course, desirable location to travel to, nice body of water to swim in, hopefully good scenery on the course, good hotels and restaurants close to the race site. With these features, I would actually prefer a smaller independent race to a 70.3. A later than 7 a.m. start would also be great.
To me, a big 70.3 turns a bit too much into a circus with it being a pain to park, the courses potentially being too crowded, and so much competition that non-elite age groupers are really not racing against anyone.
I have enjoyed the M-dot races I have done, but I enjoy the smaller races more. In a smaller race, I have a chance to try and race for an age group award, I don’t get clubbed all swim, drafting is not an issue, I get to be alone on the course at times or have someone a few hundred yards ahead to try and reel in on the run instead of being surrounded by dozens of other runners. It just feels like more of a race to me.
I have done Firmman in Rhode Island. It was a fantastic race and it appeals to me much more than the Rhode Island 70.3, with needing a shuttlebus to get to the race start at the crack of dawn, and a thousand more racers on the course. I have done Eagleman, and it was a great race. But Chesapeakeman, on the same course, with 2000 less triathletes was a far, far better experience. Some other non M-dot halfs that I thought were really great were the Cleveland 1/2, Mooseman, the Mountaineer Half, and Vermont Sun. Also, a race like the Harriman 1/2 is really great - it is on a super hard course and has a real grass-roots feel to it.
One thing that might transcend the m-dot is if your race has some kind of signature feature that draws people. SOS is not an m-dot and does not advertise, but through positive word of mouth, one cannot even get into that race anymore. I’m not sure what kind of numbers Savageman gets, but they do a great job advertising the difficulty of the course. Same with Harriman, which generally sells out, or the Auburn Half.