I never had the opportunity to use showcases, because I sell jewelry, and those slots would sell out in a manner of minutes, and I was never on (at midnight?) when the slots would go up for sale.
I honestly think the showcase system was heavily flawed, mainly for the reason I just listed. It might have worked for some people selling some things, but certainly wasn't ideal for everybody. So I think Search Ads are probably an improvement over that.
Now I can't say that I'm happy with Search Ads, either.. I'm still undecided on that. But when I don't think that it's worth it, I just take that money over to facebook or somewhere else to do an ad campaign for a bit. Just advertise however works best for you -- you may find advertising somewhere else entirely would be money better spent. You never know until you try. :)