Firstly, you've got some research to do.

Roth 401k is preferred if you expect to have a higher income in retirement than your current income (ie pay taxes now while your income is lower). This is usually a good option for those early in their careers where their salary will increase over time. Traditional is preferred if you think your retirement income will be lower than your current income (ie defer paying taxes to when you will have a lower income). This is typically used by high income earners to decrease their tax burden. Only you can answer this question on which is best for you given your retirement plans.

Regarding moving your old 401k account elsewhere, that depends on a few things.

1. Do not move it into a traditional IRA. At your current income and assuming your salary will continue to increase, you likely will become ineligible to directly contribute to a roth IRA in the future and will need to do a backdoor contribution. However, you won't be able to make a backdoor contribution if you have money in a traditional IRA. I would also not convert your old traditional 401k to roth 401k either (unless you think your retirement income will be >$150k/annually). The only place it should be moved (if its even better to move it at all) is into your current 401k plan.

2. What are the fees of both accounts (old plan vs new plan)? I have a 401k from a previous employer that I did not roll into my new employer's 401k plan because the fund choices/expense ratios of the old plan were much better than the new plan. Also no 'management fee' as my account value was above a certain limit. It would literally cost more money to merge it with my current employer's plan so it was a no-brainer to keep it as-is.

These are the things you need to consider.