Within the context of a Nuzlocke: A 'best team' is highly dependent on what you start with, the rules that you set for yourself, and what you manage to catch. Generally speaking however, for Red/Blue/Yellow, here are some Pokemon that deserve mentions within the context of a RBY a Nuzlocke.
In Red/Blue, Bulbasaur is the best starter for a Nuzlocke. By a mile. For best results: Delay evolving it until level 41, to gain access to Sleep Powder ASAP (and give it the Body Slam TM for some extra damage in the mean time). If you grant yourself the option to choose, pick Bulbasaur. If you're playing randomised, and you're lucky enough to roll Bulbasaur (like I managed to do), then well done!
If your starter is Charmander, and you lack other options for Brock, use Ember against his low-Special rock types, even if they resist it.
Pidgey has Sand Attack, which offers an alternative way to get through Brock's Gym, in the event that you lack any Pokemon with Super Effective moves against his stuff. Nidoran (F), Spearow & Pikachu also have Growl, which can help as well. Additionally, the Water Gun TM in Mt Moon can be taught to Rattata, Jigglypuff, Clefairy, and Nidorina/Nidorino, if you lack 'Geodude coverage' by this point.
If you allow for 'guaranteed in-world' Pokemon to be selected for your team: Magikarp in Mt Moon Pokemon Centre (which with some effort can be evolved into Gyarados and taught Water Gun and/or BubbleBeam after Misty), Diglett from Diglett's Cave, Eevee in Celadon Mansion (might want a dice roll to pick an evolution, and if not I'd pick Jolteon), Snorlax on Route 16 or 12, and Lapras in Silph building, are all great 'guaranteed picks' for any team.
For a final team makeup, you're mainly aiming for something that can beat: - Lorelei (Water types mainly despite being 'the Ice lady'), Bruno (Fighting Types + Onix), Agatha (Poison & Ghost types), Lance (Gyarados + Dragon types), and your Rival (Flying in RB/Electric in Y, Psychic, Ground, Water, Fire, Grass). A Grass/Ground/Electric/Ice core can beat all of these (e.g. Venusaur, Jolteon, Lapras, Dugtrio), so I would strongly advise aiming for these 4 archetypes within your team!
Within the context of a Nuzlocke: A 'best team' is highly dependent on what you start with, the rules that you set for yourself, and what you manage to catch. Generally speaking however, for Red/Blue/Yellow, here are some Pokemon that deserve mentions within the context of a RBY a Nuzlocke.
In Red/Blue, Bulbasaur is the best starter for a Nuzlocke. By a mile. For best results: Delay evolving it until level 41, to gain access to Sleep Powder ASAP (and give it the Body Slam TM for some extra damage in the mean time). If you grant yourself the option to choose, pick Bulbasaur. If you're playing randomised, and you're lucky enough to roll Bulbasaur (like I managed to do), then well done!
If your starter is Charmander, and you lack other options for Brock, use Ember against his low-Special rock types, even if they resist it.
Pidgey has Sand Attack, which offers an alternative way to get through Brock's Gym, in the event that you lack any Pokemon with Super Effective moves against his stuff. Nidoran (F), Spearow & Pikachu also have Growl, which can help as well. Additionally, the Water Gun TM in Mt Moon can be taught to Rattata, Jigglypuff, Clefairy, and Nidorina/Nidorino, if you lack 'Geodude coverage' by this point.
If you allow for 'guaranteed in-world' Pokemon to be selected for your team: Magikarp in Mt Moon Pokemon Centre (which with some effort can be evolved into Gyarados and taught Water Gun and/or BubbleBeam after Misty), Diglett from Diglett's Cave, Eevee in Celadon Mansion (might want a dice roll to pick an evolution, and if not I'd pick Jolteon), Snorlax on Route 16 or 12, and Lapras in Silph building, are all great 'guaranteed picks' for any team.
For a final team makeup, you're mainly aiming for something that can beat: - Lorelei (Water types mainly despite being 'the Ice lady'), Bruno (Fighting Types + Onix), Agatha (Poison & Ghost types), Lance (Gyarados + Dragon types), and your Rival (Flying in RB/Electric in Y, Psychic, Ground, Water, Fire, Grass). A Grass/Ground/Electric/Ice core can beat all of these (e.g. Venusaur, Jolteon, Lapras, Dugtrio), so I would strongly advise aiming for these 4 archetypes within your team!