First of all, I have tried both and not really seen any results from either.
I honestly feel that if your diet is very protein rich, (1g per lb bw/day), you are getting more than enough glutamine.
Therefore I don't do either.
BUT, if you DO insist on taking glutamine, the science and economics behind it really point towards glutamine, if only becase the cheapest glutamine and the cheapest glutamine peptides are about the same price, yet the glutamine peptides have at most 1/3 of the glutamine in pure glutamine (though it's probably more like 16% or so). There is no evidence either that the glutamine in glutamine peptides is absorbed three times better. If anything the evidence says pure glutamine is absorbed more efficiently.
JC
PS use the search function, you will find everything I have read and much more I'm sure.