Piper Sandler believes Adobe (ADBE.US), MongoDB (MDB.US) and Salesforce (CRM.US) are the best stocks to invest in cloud software stocks.Analysts led by Brent Bracelin at Piper Sandler said: "We recommend that large growth investors take more risk and add to their 'MAC' positions." MAC refers to Adobe, MongoDB and Salesforce.Bracelin added: "These are stocks that have underperformed the market, with average shares still 26% below their 52-week highs, despite healthy product and profit catalysts, and favorable risk-reward."MongoDB could accelerate growth after hitting a low in the second quarter. The stock has fallen 29% this year. Piper Sandler expects it to recover 29% of its fall to $335 over the next few quarters, as the company remains a high-quality database franchise.Adobe is also similar, and could recover this year on the back of its latest artificial intelligence products.Piper Sandler said: "The new innovation product cycle is underappreciated, which could help reinvigorate growth."Salesforce has risen 9% this year, but has fallen nearly 5% over the past six months.Bracelin said: "We expect Salesforce to rise 11% to $325, and 39% to $405 in a bull case."Piper Sandler rates Adobe "Overweight" with a target of $635; "Overweight" Salesforce with a target of $325; "Overweight" MongoDB with a target of $335.