I love this topic question. :)
With only the Pokemon's emotion dialogues to go by and of course, the Lady in Goldenrod who can tell you how your Pokemon feels about you, how else can you tell who 'loves you the most'?
With that in mind and going by how my Pokemon act towards me and the like, I would have to say that it is probably my 'original' group comprising of: Bayleef (who started out as a Chikorita), Furret (who started out as a Sentret), Noctowl (who started out as a Hoothoot), Onix, Togetic (who started out as a Togepi), and Gengar (who started out as a Gastly) who love me the most.
They have been with me the longest and Gengar aside, they have never been given any reason to dislike me. To get Gengar, I had to trade my Haunter and then get her back, so when I got her back, she no longer loved me, but that's simply a given.
But in all reality, the group of Pokemon I continually work with (in alphabetical order):
Ampharos, Bayleef, Furret, Gengar, Gyarados, Jolteon, Machoke, Noctowl, Onix, Scyther, Steelix, and Togetic (I will be adding a few others to the group shortly) all cuddle up to me on a regular basis and look at me with adoration and continually find things for me and continually tell me that they put in extra effort.
So I guess for me, it's really hard to say who loves me the most.
Who -I- love the most is also hard to say, but I have to admit that I still favor my 'original' starting gang and the Furret especially is just too darn CUTE when she eeeps and hops around and cuddles and adores.