I would choose AEZS. They have a larger pipeline and the pipeline has lots of excellent potential. KERX has a small pipeline with another drug in for approval, but they have stated that they are for sale and may be bought out next year if perfisone is approved by the FDA. In a couple of years, AEZS could be much higher with positive approvals.
Depends on what you are in this for. If you are only interested in Perifosine, definitely Keryx. They will have a much bigger pop on Perifosine approval. If you are more interested in long term appreciation and a more robust pipeline, then you are talking AEZS. As noted in another post by Bioinvestor, they have a very solid pipeline, and AEZS-108 has real blockbuster potential.
Just remember that either way, these are both still speculative biotechs, and even though prospects are good,there is no guarantee that either Perifosine or 108 will gain FDA approval. Invest accordingly.