Junk bonds have enjoyed a rally since the start of the year but investors are facing a dilemma.

Should you buy larger, more liquid bonds that have already risen significantly, or buy smaller, illiquid bonds that have an attractive price?

Barclays Capital says triple-C rated bonds — the riskier segment of the junk space — are beginning to catch up with less risky issues because higher rated bonds have increasingly run into “call constraints”.

(For non bond geeks: Some corporate bonds have an embedded call option that allows the issuer to redeem the debt before its maturity date. )

Barclays says as of Wednesday’s close, 71 percent of callable BBs and 57 percent of callable single Bs were trading above their next call price, compared with just 29 percent of CCCs.