If Allen has an opening in the North Atlantic Conference you should take it. In all D3 worlds, it is one of the top three (probably 3rd). At least half the conference makes the NT and the conference RPI is over .6000 each season.
By RPI the 2nd best conference in Allen has been the NESCAC for quite a while. They currently have two openings and the conference features the current national champion.
Personally, if the North Atlantic isn't full, I'd recommend joining the Minnesota Intercollegiate. They have had trouble filling up human spots but they have arguably the two best Allen D3 coaches in Rails and bluespruce, they just got a returning legend in joelhall32 to sign up after being away for 30 seasons, and they have a few additional coaches that are quite good and have been around for 20+ seasons.. I think a full MIAC would give the NAC a run for its money. Right now there are three open spots in the MIAC.