It's between Pichu and Typhlosion, as for which I'm not sure. Pichu is solely because of how much I enjoy them in Smash and Typhlosion is from the nostalgia of having HGSS as one of my first games.
Ooh tough cgoice. Ill just say Totodile cause it evolves into a beast and I was a Totodile once in PMD
Chikorita, Ledyba, Spinrack, Mareep, Hopip, Pineco, Sunkern, Wooper, Natu, Shukel, Dunsparce, Swinub, Murkrow, Houndour, Umbreon, Sneal, Misdrevus, and Larvitar...... Kind of tells you my favorite typings XD some outliers though with Mareep, Wooper, Natu, and Dunsparce