Romancecar from Shinjuku · the standard route
The Odakyu Romancecar Limited Express runs direct from Shinjuku Station to Hakone-Yumoto in 85-90 minutes (¥2,470 reserved seat). No transfers, large windows, snack/drink trolley. Departures are roughly hourly all day. Reserve a few days ahead for weekends and peak periods, especially the Saturday morning and Sunday evening trains. Buy on the Odakyu site or in person at Shinjuku.
JR Pass holders · the Tokyo Station option
From Tokyo Station: take the Shinkansen Kodama or Hikari to Odawara (35 min, JR Pass valid), then transfer to the Hakone-Tozan Line local for Hakone-Yumoto (15 min, separate fare around ¥320). Total under an hour — faster overall than the Romancecar but with one transfer and slightly less scenic. The right pick if you have a JR Pass and don't want to pay the separate Romancecar fare.
Should you buy the Hakone Free Pass?
For a Yumoto-base trip, almost always yes. The Hakone Free Pass (¥6,100 from Shinjuku for 2 days) covers the round-trip Romancecar (or Odakyu local), all Hakone-Tozan trains up the mountain, the cable car, the Hakone Ropeway, the Lake Ashi sightseeing cruise, and most local buses. If you do even a single round-course day trip out of Yumoto, the pass pays for itself versus buying point-to-point tickets.
Should you stay one night or two?
For a Yumoto-base trip, two nights is comfortable, one night works. One night = check in late afternoon, ryokan dinner, onsen, sleep, breakfast, walk the shopping street, head back to Tokyo. Two nights = above plus a full day for the Hakone Round Course (Tozan train + cable car + ropeway + lake cruise + bus loop). Three nights starts to repeat unless you specifically want the slow ryokan-and-walking pace.