I’d use lingo to characterize a style of speaking, characterized by words both newly-minted and appropriated for a specific meaning. For example, using drag to mean boring or tedious, bread to mean money, or man as a form of address all contribute to the lingo of counterculture in the 60s.
Jargon refers to a technical vocabulary that is shorthand for complex or elaborate concepts and practices. In technology, for example, it’s often characterized by acronyms and other terms coined by inventors and innovators. In law, medical practice, and academic research, it’s a combination of terms and concepts owed to history that are often anchored to their language of origin.
Wiktionary's definition of jealous notes,
Some usage guides seek to distinguish "jealous" from “envious”, using jealous to mean “protective of one’s own position or possessions” – one “jealously guards what one has” – and envious to mean “desirous of others’ position or possessions” – one “envies what others have”. However, this distinction is not reflected in usage, as reflected in the quotations of famous authors ... using the word jealous in the sense “envious (of the possessions of others)”.
Wiktionary gives Twain and Wilde as examples. Plenty of other historical examples exist, such as this 1888 piece noting that
these colonies are bitterly jealous of each other’s position
Interestingly, Etymonline also discusses about jealous that
Most of the words for 'envy' ... had from the outset a hostile force, based on 'look at' (with malice), 'not love,' etc. Conversely, most of those which became distinctive terms for 'jealousy' were originally used also in a good sense, 'zeal, emulation.' [Buck, pp.1138-9]
which may provide some clue about why envy only seems to have a negative sense, about coveting or resenting, whereas the energies of jealousy can be somewhat positive (guarding that which one loves or seeking to emulate that which one admires).
Indeed, if we look at examples of the obsolete uses of envy in Wiktionary, such as "hatred, enmity, ill-feeling," they sound worse than being jealous:
1485, Thomas Malory, Le Morte Darthur, Book X:
‘Sir,’ seyde Sir Launcelot unto Kynge Arthur, ‘by this cry that ye have made ye woll put us that bene aboute you in grete jouparté, for there be many knyghtes that hath envy to us [...].’
Ultimately, how you qualify these words (do you sigh, to indicate that your envy is merely a wistful desire? do you write that the person had a burning envy, or a playful jealousy, or a jealousy that knew no bounds?) will determine which is the stronger, or more negative, for today's speakers. As @Hal points out, either is likely to be understood.
Best Answer
According to Michael Quinion, Ologies and Isms: Word Beginnings and Endings (2002), -less words fall into two main categories: words where the -less form indicates simply "without" (as, for example, bottomless, childless, defenceless, and lawless), and words where the -less form "indicate[s] something that is unaffected by the action of the verb, or some failure or inability to carry out that action" (as, for example, dauntless, quenchless, relentless, tireless).
In contrast, Quinion says, the prefix un- usually lends the simple meaning "not" to the resulting word; but in some instances it "often has a stronger and less neutral force than just negation (so it is not equivalent to NON-): unkind can mean active cruelty rather than simple lack of kindness; to say someone is un-American can imply an active antagonism to American ways. Furthermore, with verbs, Quinion says, un- "usually has the sense of reversing some state" (as, for example, unburden, unlock, unsettle, untie).
So on a basic level, the split between -less words and un- words is the difference between "without" and "not." But in addition, Quinion suggests, some -less words imply a resistance to an embedded verb, and some un- words either express a reversal of an embedded verb or go beyond mere negation to suggest an active opposition to an embedded adjective.