Some head coaches prefer quality in their squad rather than quantity, others prefer to have strength in depth to ensure that the side will be covered if injuries occur. To get the right balance between the two is very difficult and a good squad - where those that replace injured or suspended teammates are just as good as those they are replacing - is often the difference between those sides at the top and those nearer the bottom.

Here are the four sides whose squads look in the best shape going into the 2018 season.

Hull FC

Arguably, the Airlie Birds have the strongest squad heading into 2018. Though Mahe Fonua and Gareth Ellis will be very difficult - if not impossible - to replace, Lee Radford has bolstered his ranks with Mickey Paea, Bureta Faraimo, and Hakim Miloudi. Not only is Hull's first 17 brimming with quality with the likes of Fetuli Talanoa, Albert Kelly and England international Scott Taylor, but Hull's overall squad is littered with stars.

Sika Manu and Mickey Paea, for example, will wear the numbers 21 and 23 respectively whilst there is an abundance of young talent filling the squad such as Brad Fash and Jansin Turgut whom will be eager to show what they can offer in a back-to-back winning Challenge Cup side.

Even if FC suffer with injuries, more-than capable replacements are waiting in the wings, chomping at the bit to send Hull racing to the top four once more.

St Helens

If St Helens' end-of-season is anything to go by, they will definitely be in and around the top four in 2018. And, Saints' squad makes this prediction seem even more justified. The Lancashire side have had just one departure so far - Tommy Lee - and have made just one signing - highly-rated youngster James Bentley from Bradford. The Saints' squad is therefore a settled one, and, even more importantly, it is full of both quantity and quality.

Luke Douglas, Morgan Knowles and Luke Thompson - as impressive as they were in 2017 - have still been assigned a shirt number outside the first 13.

Moreover, Saints have good replacements for nearly all positions; at half-back, for example, Theo Fages and Matty Smith will be looking over their shoulder as talented youngster Danny Richardson and the much-raved about 20-year-old Rob Fairclough sit patiently waiting for their opportunity. The depth of St Helens' squad is that good that even Regan Grace has been pushed out to number 19 in favor of Tommy Makinson and Adam Swift. Saints' academy has produced a number of stars over the years, and 2018 could well be the season that more of this talent pushes its way into the first-choice 17.

Castleford Tigers

Some Rugby League supporters may not agree with my choice to put the 2017 League Leaders in this list considering the likely two-year ban for Zak Hardaker and the signing of Championship players.

But, the Tigers' first-choice 17 and those that will likely fill in case of injury or suspension still boast those players that steered Castleford to their best-ever finish in 91 years in 2017.

Ben Roberts will take up the fullback spot in Hardaker's absence and new signing Jamie Ellis will likely partner Man of Steel Luke Gale in the halves in 2018. That leaves wonderkid Jake Trueman and - though as baffling as the signing was - Cory Aston to compete for that one elusive half-back spot alongside Gale.

Competition for places has been something which head coach Daryl Powell has prided himself on in recent years with the Tigers and 2018 will be no different. Greg Eden, Greg Minikin, Garry Lo, James Clare and Jy Hitchcox will all be battling for a wing spot whilst newcomer Joe Wardle could be competing for a centre spot with Jake Webster and Michael Shenton or, more than likely, will be aiming to take a second row spot from the likes of Mike McMeeken, Oliver Holmes and Alex Foster.

Though the Tigers' recruitment has been slated, those incoming are a step above than those leaving the club. PNG powerhouse Garry Lo, for example, represents much more of a threat than a Joel Monaghan on his last legs. James Green and Mitch Clark - though both with points to prove after less-than impressive seasons in 2017, are hungry to show what they can do and will offer more than both Larne Patrick - who was plagued by injury - and Andy Lynch - whom could no longer keep up with the pace of Super League - did in 2017.

Leeds Rhinos

Grand Final winners Leeds Rhinos will go into the 2018 season without Hull KR-bound Danny McGuire as well as the retired Rob Burrow. But, on paper, the Rhinos' squad looks even stronger than it did in 2017.

With Richie Myler and Brad Dwyer - both with many years still ahead of them - replacing stalwarts McGuire and Burrow, Leeds may not feel the loss of the two club legends too much.

The Rhinos' strength-in-depth is also something to envy; teenage star Jack Walker finds himself with the number 24 shirt whilst the likes of Brett Ferres, Keith Galloway and Jimmy Keinhorst all find themselves ousted from the first-choice 17. Leeds' conveyor belt of youth has consistently churned out superstars in the past decade and 2018 could be the time to shine for youngsters Mikolaj Oledzki, Josh Jordan-Roberts and Harry Newman.