In fact it is difficult to assess just which club is in the worse slump. City have meekly surrendered any hopes of retaining their title or winning some silverware by losing eight games from their last 14 in all competitions during the most crucial stage of the campaign.
For Manuel Pellegrini's chokers it can be traced all the way back almost three months to the day on Sunday January 18th when the Blues were comfortably beaten 2-0 by rivals Arsenal at the Etihad. Arsene Wenger's side had been written off as title challengers and were struggling to convince people they had what it took to get in the Champions League places, mainly due to their inability to win away from home.
But that's exactly what they did that day and the contrast in performances and results for both sides since has been marked.
It set City on a downward spiral and the following weekend, that famous day of FA Cup shocks, saw them beaten 2-0 again at the Etihad, this time by Championship promotion hopefuls Middlesbrough.
They picked themselves up to earn a good point on their travels to title rivals Chelsea next but followed it up by dropping another two points at home to Hull City.
Pellegrini was under intense pressure now but emphatic back-to-back wins, 4-1 at Stoke City and 5-0 at home to Newcastle United, seemed to get their season back on track ahead of a Champions League clash with Barcelona.
A 2-1 home defeat to Lionel Messi and Co saw the black cloud overhead again, though. And when Liverpool beat them by the same scoreline next time out, their Premier League hopes were well and truly floundering.
In the next six games the season disintegrated, shocking even the most grounded of City fans. Defeats to Burnley, Barcelona, Crystal Palace and last week's 4-2 Manchester derby humbling has speculation raging over the future of Pellegrini and a number of the club's players.
But if City needed a pick-me-up, surely they couldn't wish to be facing a side more likely to hand it to them on a silver platter today?
For the first time in months Pellegrini is facing a manager who is probably under as much pressure in Sam Allardyce. And they are facing a team with little but pride to play for.
The Hammers, who had been flying high in the Champions League places for the first half of the season with a fresh new squad and approach, have won just twice in the league since Christmas. The East Londoners' slump goes further back than City's. From their last 19 Premier League and FA Cup games the Hammers have won just four times. And all of those wins have been hard work. They beat Everton on penalties at Upton Park despite playing against 10 men for much of the match having already taken the lead.
They toiled against League One Bristol City and needed a controversial goal from sub Diafra Sakho to get over the line. A 3-0 home victory over Hull doesn't tell the whole story from a game where the Hammers played one of their worst halves of football this season before turning things around after half-time.
Their most recent win, 1-0 at home to Sunderland, came in the last couple of minutes and had a touch of fortune about it as Nene looked to have fouled a Mackems defender in the build up.
Hammers fans would argue they are due the rub of the green. But most would be honest enough to point back to Boxing Day to chart the start of their tribulations. The in-form Hammers were away to fierce London rivals Chelsea and star players like Alex Song and Sakho were flying.
But Allardyce, mindful of the busy festive fixture list and targeting what he deemed a more realistic opportunity to earn three points at home to Arsenal two days later, made wholesale changes to his side.
Allardyce would have believed the side he put out was capable of earning a result. But the negative approach - the Irons had no shots on target in the entire game - was seen by fans as surrendering an easy three points to a club they love to hate while simultaneously squandering the club's precious momentum.
Two days later they, rather unfortunately it has to be said, lost 2-1 to Arsenal. There have been good performances that should have delivered wins since. But one win in two and a half months since tells its own story and underlines just why Allardyce is feeling the heat at West Ham.
A season that promised so much but will deliver little other than a stress free cruise to midtable mediocrity has put the 60-year-old's head on the managerial chopping block.
Last time out the Hammers were beaten 2-1 at Leicester City ahead of what is a crucial game for very different reasons today at the Etihad. If West Ham's players want Allardyce to keep his job, today is the day to prove it and with every Premier League place worth upward of £1 million, it is crucial to the club's owners.
City need the three points to try and cling on to their Champions League place and so you feel anything other than a home win would be a huge shock and the final nail Hammered into Pellegrini's hopes of hanging on to his job.