How do you indentify VMs that generates the most IOPS? With the vSphere Client?

No, we do it in PowerCLI 😉

I found a very good script from LucD and created a function around.

function Get-VMMaxIO
{
  <#
      .SYNOPSIS
      Get your VMs with max. IOPS 
      .DESCRIPTION
      Get your VMs with max. IOPS (read & write Avg.)
      You could work with the parameters vHost,Cluster or DataCenter to determine the ESXi Hosts. (default = all Hosts)
      With the parameter minutes, you could change the period of time (default = 1)
      With the parameter top, you could change the number of VMs listed  (default = 10)
      .EXAMPLE
      Get-VMMaxIO

      Get-VMMaxIO -vHost myHost01
      Get-VMMaxIO -Cluster myClusterA
      Get-VMMaxIO -DataCenter myDataCenterA

      Get-VMMaxIO -vHost * -minutes 10 -top 15

      .Sample Output
      PS C:\Users\myUser> Get-VMMaxIO -Cluster * -minutes 1 -top 5

      VM   Datastore         IOPSMax
      --   ---------         -------
      myVM01 MyDataStore01   18,75
      myVM02 MyDataStore02    6,85
      myVM03 MyDataStore01     5,8
      myVM09 MyDataStore04     3,4
      myVM15 MyDataStore04     3,2
      
  #>
  [CmdletBinding()]
  param
  (
   
    [Parameter(Mandatory=$false, Position=0)]
    [System.String]
    $vHost = "",
    
    [Parameter(Mandatory=$false, Position=1)]
    [System.String]
    $Cluster = "",
    
    [Parameter(Mandatory=$false, Position=2)]
    [System.String]
    $DataCenter = "",
  
    [Parameter(Mandatory=$false, Position=3)]
    [System.String]
    $top = '10',
    
    [Parameter(Mandatory=$false, Position=4)]
    [System.String]
    $minutes = '5'
  )
  
  
  #Check which Variable is filled
  if([string]::IsNullOrEmpty($vHost)) {            
    #Write-Host "Given string is NULL or EMPTY"
    
  } else {            
    #Write-Host "Set vobject" 
    $vobject = (Get-VMHost $vHost)  | Sort-Object -Property Name              
  }
  
  if([string]::IsNullOrEmpty($Cluster)) {            
    #Write-Host "Given string is NULL or EMPTY"  
  } else {            
    #Write-Host "Set vobject" 
    $vobject = (Get-Cluster $Cluster| Get-VMHost)  | Sort-Object -Property Name            
  }
  
  if([string]::IsNullOrEmpty($DataCenter)) {            
    #Write-Host "Given string is NULL or EMPTY"
    
  } else {            
    #Write-Host "Set vobject"
    $vobject = (Get-DataCenter $DataCenter| Get-VMHost)  | Sort-Object -Property Parent,Name              
  }
  
  
  
  
  
  
  $metrics = 'disk.numberwrite.summation','disk.numberread.summation'
  $start = (Get-Date).AddMinutes(-$minutes)
  $report = @()
  
  $vms = ($vobject |Get-VM) | where {$_.PowerState -eq 'PoweredOn'}
  $stats = Get-Stat -Realtime -Stat $metrics -Entity $vms -Start $start
  $interval = $stats[0].IntervalSecs
  
  $lunTab = @{}
  foreach($ds in (Get-Datastore -VM $vms | where {$_.Type -eq 'VMFS'})){
    $ds.ExtensionData.Info.Vmfs.Extent | %{
      $lunTab[$_.DiskName] = $ds.Name
    }
  }
  
  $report = $stats | Group-Object -Property {$_.Entity.Name},Instance | %{
    New-Object PSObject -Property @{
      VM = $_.Values[0]
      Disk = $_.Values[1]
      IOPSMax = ($_.Group | `
        Group-Object -Property Timestamp | `
        %{$_.Group[0].Value + $_.Group[1].Value} | `
      Measure-Object -Maximum).Maximum / $interval
      Datastore = $lunTab[$_.Values[1]]
    }
  }
  
  $report | Sort-Object IOPSMax -Descending | select VM, Datastore, IOPSMax -First $top
}