"Neither institutional investors nor the stock market appear to be impressed with either Diamond Shamrock Corp.'s proposed restructuring or T. Boone Pickens's all-cash bid for the company.</br></br>Many institutional investors, who combined own almost 10% of Diamond Shamrock, say neither choice seems to represent a significant improvement over the stock's current value.</br></br>""It's going to be a difficult choice right down to the wire,"" said an executive of one of Diamond's largest shareholders.</br></br>As previously reported, the Dallas-based energy concern on Monday announced a major restructuring plan that calls for splitting the company into two and buying back 18% of its shares for $17 each. Mr. Pickens muddled the picture on Wednesday by making his third bid to buy the company, this time proposing to acquire the 105 million shares he doesn't already own for $15 a share, or about $2 billion.</br></br>Mr. Pickens asked Diamond Shamrock's board either to accept his offer or allow shareholders to vote on the two options. He requested a response by next Wednesday."