How deep is your tank?
Some earlier models LED units could not penetrate light down to 600 - 700mm. Nowadays with much more powerfull units and lenses its not a problem anymore and they are basically equal to MH globes in that regards.
Running cost, depending on the LED unit, can be more than T5. Example comparing 6*54W T5 unit to Radion Pro, at 185W. But you need at least 2 Radion top cover the same space as 6*54W would. Total power consumption on th T5 unit is 324W and on the double Radion 370W. Depending on the lenses, maybe a third Radion, and you are at 555W. Using a lot more than the T5 unit. But I do admit, comparing Radion Pro to a T5 is not really a valid comparison. Price wise the Radion units will be a lot more expensive than the T5. T5 would also give less light, depending on the running temperature and reflectors used.
Big difference comes in that you do not need to buy globes with LED route. Top quality globes can go 8 months or longer. Reeftek is cheap, but needs to be replaced by 6 months, again, depending on the hours it run per day. 6 month old Aquamedic T5 globes push out more PAR than brand new Reeftek.
If you are setting up a tank. I would first go with a secondhand T5 unit. Rather spend more money on the best skimmer for the size system.