Depending on how much , when , were, and how you dive they both have good and bads.
I would say steel if you are only going to own 2 or 4 tanks.
Please whatever you use keep them inspected and clean, if you are using them a lot , like each weekend for a wile get them looked at each 6 mo.
The 1 year vip that most think is bs can be even to long.
I worked at dive shops and have see 1000s of tanks and even divers get sick from off sight fills at places we thought were OK to use.
Most shops will vip for 5-10 bucks less than what you paid for lunch.
And some will even check at 6 mos for free if you are using the shop for gear and travel. If not find a good shop, it only takes 2 min tops for a good tech to do you this service.
Know your air supply,its your life we are talking about.
We can live for WEEKS without food,DAYS without water,and only a moment without AIR.