Thermo Fisher Scientific Inc. shares slid 1.9% Monday, after Goldman Sachs downgraded the stock to neutral from buy on valuation grounds. Goldman removed Thermo Fisher from its Americas Conviction List and added Agilent Technologies Inc. , which it now deems its top pick in life science tools and diagnostics. Agilent shares rose 0.5%. "We see this as an opportunistic time to make the switch to A given the set-up and valuation, with Agilent providing a rare Tools opportunity to own an accelerating growth story at a reasonable valuation with untapped capital allocation upside that could potentially be unlocked by the new CFO in our view," analysts wrote in a note. On Thermo, "we believe our thesis for deal-driven accelerating growth and margin expansion has been more appropriately reflected in valuation while the company faces a difficult set of comps starting in 4Q18," they wrote. Goldman is still positive on the fundamentals of both companies, and expects beats and raises in the next few quarter. Analysts raised their stock price target for Agilent to $82 from $77, but kept its stock price target for Thermo at $250. Thermo shares have gained 29% since they were added to Goldman's Conviction List. Shares have gained 25% in 2018, while Agilent has gained 3.3%. The S&P 500 has gained 8%.