hi, i ve been to both island. in tioman, i was staying at Tioman beach resort. as for redang, i was staying at laguna redang resort. below are the comparison of these 2 places.
accommodation - both resorts are great. only diff is everything in tioman is so cheap, in terms of F&B. much much cheaper than in redang. esp. alcohol

redang is more to tourist.
transportation - tioman win. tioman is much more accessible than redang from spore. the journey from spore to tioman, took about 6 hrs. ( 4 hr bus journey + 1.5 hr ferry trip) ; as for redang, took about 12 hrs ( 10 hrs of bus ride + 1.5 hr ferry). if u r bringing kids along, dun think they gonna like it. by the time u reach redang, u r damn tired already..
activities - u may expect to have the same activity in both places. snorkeling n more snorkeling.. no expect of waterski. lot of sun burning..
scenery - definitely redang, beautiful beach, beautiful sea ( clear blue water), nice coral, uncountable fishes.
hope all these informations are useful to you.. enjoy.