I assume you wanted a fluffy answer (and I answered something similar here in a fluffy way) I mean I have an OTP tag that is dominated with Lestat/Louis and I was all well and prepared to answer you as such, but when I really thought about it… and was talking about it with thelionscrimsonclaws…

I remembered this quote:
“I don’t like myself, you know. I love myself, of course, I’m committed to myself till my dying day. But I don’t like myself.“ – Lestat de Lioncourt, Memnoch the Devil.
And I feel like I doubt whether canon!Lestat can truly trust any of all his lovers to be the ONE TRUE LOVE. I think his one true love is himself, and his mission to find the answers he needs, so really, LIFE ITSELF.
Lestat/Life = OTP!
No one is better than he is at beating himself up and then healing from it; he’s had to rely on himself and his own judgment for most of the big decisions in his life. For better or worse.
Also, I think Lestat requires a lot of different interactions with different lovers, no one individual seems able (or willing) to satisfy all these myriad needs. Everyone who loves Lestat intimately seems to accept that they will have to share him, but he has an enormous amount of love to give, there seems to be a limitless supply for all of them ❤
Spoilers ahead…
Of the ones you mentioned, each one was a unique relationship. He’s never the same exact person, he behaves differently in different pairings.
Louis: If there were a One True Love, it would be Louis. Their relationship, while volatile, even lethal at times, is something they both cleave to. Louis has learned from Lestat’s example and has become stronger over time, emotionally and physically (although he was always somewhat of a BAMF). Lestat has gained the skills of inner peace and patience from Louis’ example. Their chemistry has been the best of any pairing; they’re not two halves of one whole, but two individuals who challenge each other, who strive to surprise each other still, and in my opinion, that’s what the best relationships do.
However,
Louis tried to check out of the series w/out permission at one point, and well… that can’t be ignored.
Nicolas was Lestat’s first real long-term relationship at a time when Lestat desperately needed love and nurturing and wanted to give it back, too. Nicolas is the first person who really listened to him and they both helped each other immensely… but I don’t think that relationship could ever really work, because deep down Nicolas and Lestat always wanted different things out of life.
Akasha used Lestat. She held him in captivity and drugged him on her blood and her mental illusions, keeping him in a disoriented state by screwing with his Deathsleep patterns. She made him believe it was love, but it was really more a form of addiction. She needed him as a pawn in her grand scheme, both bc he’s a total studmuffin and also to win over the vampires that were loyal to him. She said to him that he would be her “instrument:”
“You are my only true companion, my finest instrument…. But as the stars are my witness, you will aid me in my mission. Or you will be no more than the instrument for the commencement, as Judas was to Christ. And I shall destroy you as Christ destroyed Judas once your usefulness is past.” – Akasha, Queen of the Damned.
So I wouldn’t call Lestat/Akasha a loving relationship, but hey, if you like it, that’s fine, too, I’m a #Ship and let ship girl!
Rowan Mayfair – to be honest, I can’t remember much of this pairing except that Lestat seemed captivated by her for no apparent reason other than that she was a strong woman and had a kind of tortured soul, which he recognized as being like his own. He promises her the Dark Gift:
“And the night will come when we’ll share the Blood. I promise you. The Dark Gift will be yours.” – Lestat, Blood Canticle
But AR diverted from canon with Prince Lestat, essentially rendering the Rowan/Lestat ship null and void. AR decided to sink that ship. I couldn’t really envision Rowan as being part of the coven, and it would be painful to see Louis shoved aside YET AGAIN to make way for YET ANOTHER fledgling.
…Fortunately David Talbot hasn’t minded being relegated to the background, and only getting brief moments of (dubcon) intimacy from Lestat. David knows he has to share.