Unless you travel at 7 a.m., you will always find some vacant seats in 1st class. For us, the locals, it is very uncommon to reserve seats on Swiss trains. Our trains are mass transit, we use it like buses in cities. As a result, we love the liberty of using trains at will: You show up at the station, you check the departure board for the next connection to your destination, you note the platform, you head to the platform, you get on the train, and you enjoy the ride.
You are welcome to reserve seats as an optional action, but you could easily save this money: Seat reservations in trains and dining cars. | SBB
In any case, check for trains with direct service from Zurich Airport to Visp (IC 8). They are very convenient. Try to be seated on the left hand side for a great scenery of the Alps and Lake Thun.