I don't like having six pokemon, especially in Gold, because with the super-weak wild pokemon and the lack of a vs seeker, it is too much hassle to keep six pokemon up to scratch. So yeah, when I last beat heartgold I had
Nidoking (lvl 50?-ish)
Kangaskhan (lvl 52-ish, I used it for outrage against lance)
Ho-oh (lvl 50-ish)
I also had Red gyarados as a hm slave and to absorb damage while I heal ... and I think that was it ... yup.
This time 'round, I'm using stone evolutions, so I have growlithe, gloom, poliwag and nidoran female at present, and have to decide between bellossom and vileplume (leaning towards vileplume)