Are Aviva plc, GlaxoSmithKline plc and Royal Dutch Shell plc the FTSE 100's best bargains?

Today I'm looking at three FTSE 100 (INDEXFTSE: UKX) stalwarts and asking: are these stocks bona-fide bargains or hazardous value traps?

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All-round value

I'm convinced insurance giant Aviva(LSE: AV) is one of the best big-caps out there for investors seeking stunning value.

Huge restructuring in recent years has seen the business get a grip on excessive costs, shed non-core assets and concentrate on its key growth regions.

This heavy lifting is expected to get earnings moving resolutely higher from this year onwards -- Aviva's bottom line is predicted to advance 108% and 10% in 2016 and 2017, respectively. Consequently the insurer deals on ultra-low P/E ratings of 8.3 times and 7.6 times for these years, comfortably below the yardstick of 10 times or below that illustrates stunning value.

On top of this, Aviva also promises massive rewards for dividend chasers, its terrific cash-generative qualities -- allied with the acquisition of Friends Life -- significantly bolstering its balance sheet.

As a result, dividends of 23.6p per share for this year and 26.4p for next year are currently expected, leaving Aviva with eye-popping yields of 5.6% and 6.3% for these periods.

Medical marvel

While GlaxoSmithKline's(LSE: GSK) 'paper' valuation may not be as attractive as Aviva's, I believe the pharma play is also a delicious stock selection at current prices.

GlaxoSmithKline has seen earnings slide during the past four years as exclusivity lapses across key products have dented revenues growth. But with the firm's product pipeline performing ahead of schedule, and global healthcare investment steadily accelerating, things are undoubtedly looking up for the years ahead.

Indeed, GlaxoSmithKline is expected to return to earnings growth this year with a 15% advance. And a further 4% rise is predicted for 2017.

And while subsequent P/E ratings of 16.4 times and 15.8 times may sail outside the big-cap average of around 15 times, I reckon GlaxoSmithKline's hot growth prospects still make it a bargain at the moment.

Besides, GlaxoSmithKline's pledged dividend of 80p per share through to the end of 2017 -- yielding a splendid 5.6% -- more than makes up for the pharma ace's average earnings multiples.

Driller in danger?

At first glance fossil fuel giant Shell(LSE: RDSB) may also appear a decent bet for those seeking blue chips with brilliant value.

Sure, City predictions for a 35% earnings slide in 2016 may create a hefty P/E rating of 23.2 times. But more patient investors may well be drawn in by Shell's far-improved P/E rating of 13.1 times for next year, brought about by a predicted 77% earnings upswing.

Many brokers remain bullish over oil prices from the end of 2016 onwards as the market imbalance begins to improve. I'm not so optimistic, however, as drastic cuts from OPEC and Russia are still to materialise, and economic cooling in the US and China casts a pall over future demand. I reckon predictions of a terrific earnings bounceback at Shell may prove horribly wide of the mark.

And this patchy revenues outlook leaves Shell's dividend projections on shaky foundations too. Rewards of 188 US cents per share are currently expected for this year and next, yielding a splendid 7.4%.

But with Shell also struggling to stop debt levels ballooning, I reckon investors should give short shrift to these buoyant estimates.

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Royston Wild has no position in any shares mentioned. The Motley Fool UK owns shares of and has recommended GlaxoSmithKline. The Motley Fool UK has recommended Royal Dutch Shell B. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.