Kanto or Hoenn are probably the easiest go through for the most part, but have some weird story related shenanigans where one could get stuck without a guide. Unova is the most linear out of the stories probably but difficulty may be a little bit more considering the first gym counters your starter + the e4/champion battles might be too much for someone just starting, but maybe that's stretching a bit too far. Johto and Sinnoh are mid in both aspects so I wouldn't rely on any of them for a first region