While choosing more days can yield better results in the short term, we recommend choosing the number of days you can realistically and consistently train. You will get worse results by choosing a training frequency that doesn't match your schedule. Choosing a lower frequency is the right decision if it means you can hit most or all of your sessions every week. Even 2 training days per week has been shown to maintain or increase strength and muscle growth.
Progressively adding more days likely leads to improved gains but eventually reaches a point of diminishing returns, meaning that for the extra work, you are likely only improving a fraction of the amount over 2-4 sessions/week. If you have 6 days to train and can recover - go for it! But rest assured that you can make plenty of gains with only a couple of short sessions a week.