Seriously don't open any cases if you want to get something good. Take that key and use it to trade up. I opened about $350 worth of cases cause I wanted to open a knife but that didn't turn out so well :P I did get a couple weapons here and there but nothing that would cover my costs. A buddy has spent $700++ and has not even come close.
Looking into trading up if you want rare skins and items, it takes longer but it's worth it as there is a sure chance you'll get what you're looking for. Also never buy anything straight from the market, you can find better deals when using keys on csgolounge or on /r/globaloffensive trade.
I just recently started betting and have made a lot more profit than I do with trading. Trading takes a long time especially if you're looking at a 1-2 key return each trade. You get lucky and make more if you trade the right items.
Here's my chart and I just started betting about a week ago. I've made more profit than I have trading but it is a lot riskier. I take what I win and sell them for keys but keep some for other bets.
If you want to know how to get into trading and what items to look for I can right up a better post.
I've broken even with trading but with betting I'm in the black
. I'm really close to getting a karambit fade.