From my experience with my 30 foot flat nose and my best friends 40 foot dog nose I can say it depends and tell you the challenges I face.
On mine we wanted an RV and less of a tiny home so 30ft was great as it is easier to store, park, drive, and camp with. Being a flat nose we had 2 extra wheel wells to deal with. The hard part is the shower. Realistically you will have a couch area, kitchen area, and queen bed... that leaves little room for a shower and bathroom. At least thats been our challenge.
My best friend has a 40ft with a dog nose and has much more freedom for his build due to the wheel wells only being in the back. His goal is much more of a tiny home setup and actually bought 2 busses.
Basically 30ft is great for an RV and guest house but anything more and I would go longer. Flat nose have more challenges due to the wheel well addition. We still managed to work around the wheel wells and have what we wanted and kept an open feel.. it's just challenging.