How long should shoes last?

I'm disappointed that the gym shoes I bought 6 months already need to be replaced. And it is not that they are worn out, the left one has got a hole in the inside back from my foot rubbing against it or from me kicking my shoes off (or maybe a combination of both, I'm not really sure) and the right one is showing signs of a hole developing. The hole in the left shoe leaves hard plastic exposed that rubs against the back on my foot, causing a blister.

The most frustrating part for me is that these are expensive, supposedly very good quality shoes. They are also really comfortable. Plus, it seems like 6 months is not a lot of time for them to be trash already. Especially considering that the most action they see is at the gym maybe 3 times a week.

I consulted with Kayhow this evening and she agreed that the current shoes are toast. Her recommendations were to (a.) buy another pair of Asics and see if the first ones were just a fluke, because I really like the ones that I have or (b.) try a pair of Sauconys (her personal favorite). I told her that I'd been perusing Zappos and found a pair of New Balances that I liked. She said that she's heard good things about New Balance, too.

But I can't decide. Recommendations?