Of all the remaining texts, Torquatus' statement at XII - 40 of Book One of On Ends might be the most clear, direct, and practical statement of the Epicurean view of the "ultimate good" - and how to achieve it - that survives to us. Until now I don't think we have a thread focusing directly on this passage so this is to serve that purpose.
It seems to me that almost every phrase of this formulation is packed with meaning, and it is well worth going through the Latin in detail. I will look for that an post it too. This is the Rackham translation from Loeb. [Cicero, M.T. (45 BCE). On Ends. Translated by H. Rackham. Loeb Classical Library. Harvard University Press: Cambridge, MA, 1914,1931.] One well-formatted internet presentation is here.
Raw English Text:
XII. The truth of the position that pleasure is the ultimate good will most readily appear from the following illustration. Let us imagine a man living in the continuous enjoyment of numerous and vivid pleasures alike of body and of mind, undisturbed either by the presence or by the prospect of pain: what possible state of existence could we describe as being more excellent or more desirable? One so situated must possess in the first place a strength of mind that is proof against all fear of death or of pain; he will know that death means complete unconsciousness, and that pain is generally light if long and short if strong, so that its intensity is compensated by brief duration and its continuance by diminishing severity. Let such a man moreover have no dread of any supernatural power; let him never suffer the pleasures of the past to fade away, but constantly renew their enjoyment in recollection, and his lot will be one which will not admit of further improvement.
Suppose on the other hand a person crushed beneath the heaviest load of mental and of bodily anguish to which humanity is liable. Grant him no hope of ultimate relief in view also give him no pleasure either present or in prospect. Can one describe or imagine a more pitiable state? If then a life full of pain is the thing most to be avoided, it follows that to live in pain is the highest evil; and this position implies that a life of pleasure is the ultimate good. In fact the mind possesses nothing in itself upon which it can rest as final. Every fear, every sorrow can be traced back to pain; there is no other thing besides pain which is of its own nature capable of causing either anxiety or distress.
Pleasure and pain moreover supply the motives of desire and of avoidance, and the springs of conduct generally. This being so, it clearly follows that actions are right and praiseworthy only as being a means to the attainment of a life of pleasure. But that which is not itself a means to anything else, but to which all else is a means, is what the Greeks term the Telos, the highest, ultimate or final Good. It must therefore be admitted that the Chief Good is to live agreeably.