Modern Emerald Best Starter: All Three Compared

There is no wrong pick, but the three starters face different early games, and in Hard mode that matters more than usual because the level caps and the boss levels leave you less room to brute-force it.

Base stats, final evolutions

Starter	Types	HP	Atk	Def	SpA	SpD	Spe	BST
Treecko	Grass	40	50	30	65	55	70	310
Grovyle	Grass/Dragon	50	70	40	85	65	95	405
Sceptile	Grass/Dragon	70	95	60	105	85	120	535
Torchic	Fire	45	60	40	70	50	45	310
Combusken	Fire/Fighting	60	85	60	85	60	55	405
Blaziken	Fire/Fighting	80	120	70	110	70	85	535
Mudkip	Water	50	70	50	50	50	40	310
Marshtomp	Water/Ground	70	85	70	60	70	50	405
Swampert	Water/Ground	100	110	90	85	90	60	535

Evolutions

Line	Evolutions
Treecko	Grovyle 16, Sceptile 36
Torchic	Combusken 16, Blaziken 36
Mudkip	Marshtomp 16, Swampert 36

The typings are not vanilla

One thing the table above makes obvious: Treecko's line is Grass/Dragon in this hack, not pure Grass. That gives Grovyle and Sceptile resistances to Water, Electric, Fire and Grass, but it also means Ice hits them for 4× — the single biggest weakness on any of the three starters. Torchic and Mudkip keep their vanilla typings (Fire/Fighting and Water/Ground), so Mudkip's one Grass weakness remains its only real problem.

The early-game matchups

Roxanne (Rock, first gym) — Treecko is the worst start here: Grass takes neutral damage from Rock and Treecko's physical bulk is the lowest of the three. Mudkip resists Rock and wins the gym comfortably. Torchic is neutral but Combusken gets Fighting moves shortly after.
Brawly (Fighting, second gym) — Torchic's line is the problem child: Fighting hits Fire neutrally and Combusken has poor Defence. Treecko resists Fighting and is the best of the three. Mudkip is neutral.
Wattson (Electric, third gym) — Mudkip's Ground typing is a hard counter via Marshtomp; Treecko and Torchic both have to bring a Ground or Grass answer from the box.

What each one is good at long-term

Swampert ends up the most forgiving: a Water/Ground typing with only one weakness (Grass), which is rare in Hoenn, and it is the best of the three against the Elite Four's Drake and against the electric-heavy mid-game.
Sceptile is the fastest of the three and the best into the water routes and against Wallace. It is fragile, so it wants the level caps in its favour.
Blaziken has the highest damage ceiling and a Fire/Fighting typing that covers Norman, Glacia and Sidney well, but it is slow to come online and the squishiest early.

The rival takes the counter

Your rival picks the starter that beats yours, so the fight on Route 103 is a matchup you will lose on paper. On Route 110 and Route 119 the rival's team gets its final evolution instead of staying mid-stage, so plan for a full-strength starter rather than the vanilla half-evolved one.

Catching the other two (and the Johto/Kanto starters)

Modern Emerald adds a new zone in the Safari Zone where the Hoenn starters can be caught, so you are not locked out of the two you did not pick — with one caveat: that zone is not available in "Original encounters" mode. Johto and Kanto starters live in their own added areas, which is what the achievements for collecting them are for.

Hard mode differs

In Hard mode your rival's starter gets a boosted ability and stat multiplier: Blaziken gains Speed Boost, Sceptile gains Thick Fat, Swampert gains Hustle — so the counter-pick is more dangerous than the type chart suggests.

Stats, typings and evolution levels read from the extracted game data; ace changes from the hack's official documentation.