All the planes you have discussed are good flying planes. The Sig Senior is a terriffic model to fly, but I don't recommend it as a primary trainer because it is basically a stick model. A trainer sometimes leads a hard life and "durablity" is a prime requisit. Consider the Sig LT 40, either kit built or ARF. It is one of the best trainers out there. I also learned on a three channel trainer 30 years ago (Sig Kadet). That was before buddy boxes and ready availablity of instructors. The Kadet was my successful trainer after I had demolished several other kits in the learning process. Following that, I built and flew a 4 channel Sig Kougar. It was re-learning all over again with some tense moments, but the plane survived my efforts.

Best bet with instruction available to you is to go 4 channel from the first. Later, you may want to get a 3 channel knock around plane to fly, just for the fun of it. Enjoy the hobby.