I found it! It's in the third book of the Robots cycle, The Robots of Dawn (chapter 2: "Daneel"), and said by Daneel, as you correctly guess (emphasis mine):
“Of a certainty, Partner Elijah. It is a pleasure to see you.”
“You feel emotion, do you?” said Baley lightly.
“I cannot say what I feel in any human sense, Partner Elijah. I can say, however, that the sight of you seems to make my thoughts flow more easily, and the gravitational pull on my body seems to assault my senses with lesser insistence, and that there are other changes I can identify. I imagine that what I sense corresponds in a rough way to what it is that you may sense when you feel pleasure.”
Perfect fanfic material, that.
To find it I had to try search strings like "happy", "happier", "happiness", "circuits", "makes me", "makes my", to no success. Right before giving up I tried "emotion", and voila!
A Spanish translation (Los robots del amanecer, by Maria Teresa Segur Giralt) is as follows:
—Sientes emoción, ¿verdad? —preguntó Baley con ligereza.
—No puedo expresar lo que siento en un sentido humano, compañero Elijah. Sin
embargo, te diré que el verte hace que mis pensamientos fluyan más fácilmente, y la
fuerza gravitacional de mi cuerpo parece asaltar mis sentidos con menos insistencia, y
que hay otros cambios que no sé identificar. Me imagino que lo que siento corresponde
aproximadamente a lo que tú puedes sentir cuando estás complacido.