So now you are at a "good" company as FO with low pay and will probably be able to upgrade to CP within max 2 years?
What will the pay increase - how much of your current FO-salary - be and what will you be flying?
How does the salary increase over time?
Going to the "National Company" as forever-FO would get you 3 times your current FO-salary??
How does that increase over time?
Would you have to move?
Would you want to move?
Does either company have a pension-scheme. etc.?
Why and where to would you want to leave either company in 2 years?
It all depends on your priorities (make a detailled list of those):
Lifestyle - Money - regardless of rank - or do you absolutely want fly as a CP?