As always brokers up and down Australia have been busy upgrading and downgrading shares included in the S&P/ASX 200 (Index: ^AXJO) (ASX: XJO).

Three shares in particular which found favour with brokers today and have been upgraded to buy ratings are below. Should you invest in them? Let’s take a look.

Fortescue Metals Group Limited (ASX: FMG)

The iron ore giant has been upgraded to an outperform rating by analysts at Macquarie according to a research note released this morning. Its analysts appear to be pleased with the buyout of BC Iron Limited’s (ASX: BCI) 75% interest in the Nullagine joint venture. As well as this, iron ore prices remain favourable and should allow the miner to continue paying down debt at a rapid rate. Whilst I would agree that Fortescue Metals is a good investment, it is on the proviso that iron ore prices remain at their current levels. But with many predicting a sharp drop in prices in the coming months as supply increases, the bumper profits it has been making could be short-lived.

Mayne Pharma Group Ltd (ASX: MYX)

A research note out of UBS reveals that its analysts have upgraded growing pharmaceutical company Mayne Pharma to a buy rating. They expect the company’s recently acquired portfolio of drugs will allow it to grow at an even stronger rate than the generic drugs industry average. I would have to agree with UBS on this one. In my opinion Mayne Pharma is one of the better investments available in the industry at the moment. With its shares changing hands at just 20x estimated FY 2017 earnings, I feel it is at a reasonably fair price for a long-term investment.

Origin Energy Ltd (ASX: ORG)

Analysts at Citi have slapped a buy recommendation on Origin following news that it has produced the maiden LNG cargo from the second of its 4.5 million tonnes per annum production trains. This has come in ahead of schedule and could be a boost to full year earnings. With oil and LNG prices looking favourable right now, Origin certainly is in a strong position to profit. Ultimately the direction those prices take in the next few months will dictate the company’s performance. I’m reasonably bearish on oil and expect it will drop lower again in the next few months. But if you’re bullish you could do a lot worse than an investment in Origin.

If you need to make room in your portfolio for any of these shares then I would highly recommend removing these wealth destroying shares from your portfolio if you own them.

3 Rotten Shares to Sell, and 1 to Buy Today

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Motley Fool contributor James Mickleboro has no position in any stocks mentioned. The Motley Fool Australia has no position in any of the stocks mentioned. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy. This article contains general investment advice only (under AFSL 400691). Authorised by Bruce Jackson.