Hoping anyone might have any experience of the 2 organisations. I am looking at planning my event and training schedule for next year and who welcome any words, advice
They are both independent brands who run middle and full iron distance races . I've not personally done any racing (yet) with these.
Challenge I think are generally a bit cheaper but are getting a lot more recognition recently. I've always heard good things.
From performance view they will be different so depends if this would be a deciding factor at all: IM have their own WC processes so you can only do an IM event to qualify (for 70.3 WC and IronmanWC (Kona) ). Challenge have also started to run a ChallengeChampionship race you can qualify for too (currently less well known). You can also use results from either to qualify in ITU/ETU middle and long distance champs.
However all probably goes down to specific distance, courses, countries you are looking for so people may be able to give their experiences on what they have done.