TCredits are usually better suited for bidding in the auctions. What i usually do is, apart from my standing order, whenever i have extra cash, i buy additional TCredits so i have more bidding chips, before locking horns with other bidders!
Simply put, anything that will earn you AVP (Action Versa Point), using your credit is your best bet. Don't spend your credits buying things, spend them playing games and earn some MRP and AVP at the same time, this way, it's a win/win!