Both Maxis SurfMore 75 (RM75) and Celcom First One 5GB (RM88) give you 5GB data. Both are also offering the same price for data add-on, therefore comparing this 2 plans will come down to how often you need to make calls & SMS.
Celcom First One 5GB gives you 60 minutes free call and 60 free SMS but Maxis SurfMore 75 has no free call or SMS. So if you are on Maxis SurfMore 75 and need 60 minutes of call & 60 SMS a month, then there's an extra RM15.60 (I take the mean price for call rate) on top of RM75, which means a total of RM90.60.
In other words, if you occasionally need to make calls and SMS (especially to other networks) then Celcom First One 5GB will give you a peace of mind. If you don't make call & SMS or make just a few in a month, then Maxis SurfMore 75 is a cheaper option.