TM4C123GH6PM: TM4C123GH6PM

It is good that you made such notice - there are significant differences between the two MCU  'families.'

Khoi Nguyen83 said:

TM4C123 vs TM4C129 so  I'm sure which one is more suitable.

Somehow the word, 'not' - escaped that sentence fragment.   (otherwise - your posting would be w/out objective.)

Comes now several suggestions to aid your selection:

• the '129 family is (both) more advanced & faster than the '123 family
• that speed comparison, 120MHz vs 80MHz - may or may not prove of use w/in your application
• you note the use of I2C & USB - it is believed that the '129 offers greater flexibility & performance - in both areas.    Again - the benefits to your APP are 'difficult to determine' w/out knowing both the (real & fine) details - required (or beneficial to) your application
• you are advised to employ the vendor's powerful & expansive 'API' - rather than coding directly w/a 'Register Manipulative' format.    Many examples exist w/in the API - speeding/easing/enhancing your efforts - providing that you 'lock onto the API.'    (in contrast - NO such examples exist w/in 'Non-API' efforts - each one provides 'Unwanted New Adventure' - and (extremely) limited tech support!
• beware that powerful as those 'API' examples are - many were written for the '123 & earlier' MCU families - and may 'not' properly accommodate the '129 devices.    This holds (especially true) for the 'Set-Up & Config. of (both)  'System Clock and I2C coding.'    
• your use of the 'Forum's Search Box' (atop this page) should enable your 'pull' of examples for (both) MCU families - to best - 'advise & inform' your programming
• it is believed that (both) schematic symbol & pcb footprint exist - the vendor is best able to provide the (fine) location detail
• you (and others) are advised to 'first' - acquire one or both 'LaunchPads' - and prototype, prove & document your design - prior to attempting a pcb implementation!    It is the rare (firm or user) who can produce a 'fully proper' pcb design - minus that prototype effort - which significantly (informs & advises) your pcb design
• it is believed that the vendor has produced several 'design guides' - these should be obtained - then seriously 'read, understood & followed'
• be mindful that 'I2C' is a 'short-range bus' - and that (external) pull-up resistors are (normally) required.    Should your 'Led Strips' extend 'too far' from your MCU - then 'I2C buffers/amplifiers' (may) be required
• you note, 'special serial GPIO data' - which proves 'beyond my (and most others') pay-grade'  -  to properly interpret and/or comment.    (but to say - 'Sticking to existing STANDARDS' - most always - proves a VASTLY SUPERIOR PATH - exceeding (any) 'User Creation.'     (even if - and especially if - such 'creation' is deemed 'SPECIAL'!)

This 'laundry list' should cover many/most of your (and others') requirements.     It is wise to note that 'slow steady (thoughtful) design' (usually) proves (far) more successful than 'rushed/desperate cobbled design.'