Fastest time spent creating a CI web application

I'LL GO FIRST:  I was hired by a company to help a customer with a 10+ year old PHP web application.  It was a team of 4 (Project Manager, SA, DB and Full Stack Developer-me).  Although the customer was nice they had no trust in what the company had promised them because everyone else who had tried to rewrite the system failed.  The system worked but it had many quirky parts to it.  For example, the reports always printed out differently based on what computer and printer was being used by the users,  they had no automated way of determining how much input was being done by the users of the system. and the list goes on.  The system was not using a  PHP framework, developed with PHP 5.x and looked like it was designed from the eighties.  I also found out that the customer was going to determine if they were going to renew the contract which was up for recompete January of the following year.  Basically, I had 6 months to deliver a new system and convince the customer to renew the contract...........Well.......CI 3.x came to the rescue.  In the end I was able to develop a new system using an open source bootstrap admin theme (Gentelella), CI 3.x, upgrade PHP 5.x to 7.x, convert all reports to PDF, WOW the customer, migrate the prototype to Production ready in 4 MONTHS (I worked like crazy).  The customer renewed the contract and became a believer.

so it's been more than 2 years I started my career as a developer, yeah I started with custom PHP, then CI3, now I have completed more than 2-3 projects using CI4, currently working on a big project for the Kurdistan government, since you are far more experienced than me, I would like to ask you a question on creating PDF, which library do you use? 

Mostly I use DOM or MPDF.

and hell yeah I am eagerly waiting for CI5 and Bonfire2  
Thanks in advance and pardon me for poor English