Looks like the initial calculations are in and unsurprisingly, Hoenn starters are pretty good.
Here are some direct comparisons of their abilities with their closest analogues. Interesting they decided to split gathering types, but Sceptile's ability still gives it a berry focus.

>Sceptile
Strong, as all Berry Burst Pokemon are. Compared to Mimikyu, they actually have similar activation rates, but even though Mimikyu can crit, Sceptile has much stronger ingredients and base berry.

>Blaziken
Surprisingly strong berry farmer due to its lower ingredient finding rate, but the calculations are affected by its Charge Energy skill. Given the both of them having max energy, Typhlosion should have an edge over Blaziken in raw berry gathering.

>Swampert
This one is a bit trickier to evaluate because Tasty Chance is actually a pretty strong skill. It still gathers more berries than Marowak, but a lot of its sheer gathering power is offset by the potential of its skill. For additional reference, a top Dedenne triggers about 6 times/day.

All are worth pursuing, but Sceptile is the top dog of this generation, and its ability will scale strongly until the end of the game.