A more direct answer would be...
In order of likelihood of positive experience in my limited personal opinion:
1) Very high quality (tested) MDMA
Used once every three months, at a maximum of 120 mg, this is the most consistently positive serotonergic drug. It is not quite psychedelic - it is an entactogen, a sort of amphetamine for your serotonergic (psychedelic) brain system. The funny thing that MDMA reveals in my view? It turns out all that psychedelic endogenous DMT stuff is basically the mechanics of your love and social brain performed in day to day life. It’s all love.
2) Mescaline
If you brew a cactus (a very easy though long procedure) this is the only “phenethylamine” psychedelic in nature. That is to say, it is the only psychedelic in nature that is structurally related to MDMA. Unlike MDMA, the cactus is not toxic to your brain, it is a physically safe classical psychedelic - but it is the most “heart-opening” classical psychedelic.
3) Ayahuasca
Super easy to prepare with a variety of legal plants, and the most perfectly clear minded and visionary psychedelic (if you can handle the nausea). This is the one that is most likely to involve a sort of deep cognitive reprogramming experience, which can be and often is extremely heart opening - but not by turbo-charging your social centers, like MDMA, or by playing upon them like mescaline. Ayahuasca is rather a deep visionary journey which can heal the most intractable of wounds through its sheer perfection of visionary energy endogenous and natural to our human brain system.
I put ayahuasca at number three, because the direct nature of its visionary activity is so direct, that its action almost seems indirect. Rather than being a socially energized experience, it is introspective. I would say there is more potential with ayahuasca, especially if you cultivated a 2 hour a day meditation practice in conjunction with it...
But if you’re just trying to jump into it without going that far in...
MDMA followed by mescaline-cactus would be your best shot for radiant heart opening.
Mescaline-cactus is far more physically healthy and safe and legal than MDMA.
Mescaline-cactus is simply the most heart-opening of the classical psychedelics.
MDMA is not a classic psychedelic, it is a purely pro-social amphetamine —— vs. a pro-industry/focus amphetamine, like Adderall or methamphetamine. Incidentally, MDMA is methylene-dioxy-METHAMPHETAMINE. See how far that MD goes?
MDMA is just the most direct pro-social thing, so if you’re just looking for that, try it out, but be really careful, test your stuff with more than one type of testing kit, it is a notoriously impure substance, and I promise you as someone who has had the real deal many a time - you do not want to waste your precious brain on shitty chemicals. Let your experiences be with the real thing - because unlike classic psychedelics, you only have limited neurological resources for experiences with MDMA and MDMA-like substances. Use your brain’s chemical resources wisely with MDMA and other related synthetic entactogens.
And yes! If the notion of parceling out your brain’s chemical resources “wisely” creeps you out, I do whole-heartedly encourage investigating either mescaline-cactus or ayahuasca instead

If you can commit to 2 hours a day while sober of closed-eyes Buddhist breath meditatation (anapanasati), you will go to places more healing than you could possibly imagine with the assistance of these plant helpers.
If you can’t handle the nausea, mushrooms are like a non-nauseous but lower grade version of ayahuasca. The same goes for LSD with mescaline-cactus. However, if you go for LSD, you’ll want to test it in a kit. In my experience with acid, even if it is really LSD, the quality can still vary... plants are much more reliable experts in chemistry than humans.
****Edit****
I guess on reflection the recommended list would be:
A 2-hour daily meditation session (for at least one month),
And then meditate while using:
Ayahuasca
Cactus
Mushrooms
LSD
MDMA