I have a number of eur/usd and gbp/usd MtM Basis swaps that are collaterized in USD. For the non-usd legs I'm constructing the muti-ccy csa discounting curve. Im using forwards for the short end of the curve and cross-currency basis swaps further out on the curve. Question is, should i be using constant notional cross currency swaps or MtM Basis swaps for this. MtM basis swaps are more liquid, so think they would be better, but not certain.The choice has a significant impact on my IR delta.