K&N have been around for a long while and have a proven track record. I just think they are old school in that other companies have used more modern filtration materials. I also don't like the oil aspect of K&N, even if you apply it as directed it does find it's way into the AFM or MAF and that cannot be good.
I use AFe Dry and haven't had any issues plus you can custom build your filter with them to suit your space, filtration and flow requirements. Expensive compared to K&N though:
Performance Air Filters