I currently have
Nidoking (killed in 2 hits by Dig)
Bellsprout (used to take the self destruct from Voltorb)
Budew (usually dies to Electrode, sometimes I take him down first)
Granbull (dies to Raichu in 2 hits)
Pigeotto (dies to Raichu in 1 hit unless he Thunder Waves instead)
Pikachu (dies to Raichu in 1 Dig)
Currently, Raichu always goes first. I cannot capture a Diglett because I cannot access Diglett Cave without first defeating Lt. Surge. An NPC blocks your path and tells you Lt. Surge is looking for new challengers if you do. If you try to go east of Cerulean City, a NPC tells you to get the Thunder Badge first. I even tried going all the way around Mt. Moon from the other side to get into Diglett Cave, but there's a Diglett that blocks your way and prevents you from entering.