Well, most of those pokemon won't last long term (unless you are looking at a NidoKing/Queen). In MY opinion, I would go with Butterfree as a first choice (Psychic FTW!!) and Mankey as a second (Primeape is helpful with Bruno...).
Asides from getting Mankey and Butterfree, there's always the long way of beating Brock which is what I used to do when I had Pikachu/Charmander. Just by using Growl enough times to weaken their attacks or Sand Attack, (e.g. via sacrificing a Pidgey), then just using up those turns to defeat him with Scratch or Quick Attack. Takes awhile, but it stopped me having to go through getting the other Pokemon.
★ Theme features 陳琳 from 痞子英雄 played by
→ 陳意涵 (Ivy Chen), who is just ♥ awesome ♥
One strategy I have heard of is to raise Pikachu to level 20 to learn slam.
Raising pokes to lvl 20 before first gym would take a lot of time and unneeded effort. Best way to get brock defeated fast, if getting 4-5 pidgeys, and spamming sand attack until they all are down. Altrough Mankey's low kick is nice too. While using Butterfree, remember than rock attacks rapes it.