Apex:dataTable -
An HTML table that is defined by iterating over a set of data, displaying information about one item of data per row. The body of the < apex:dataTable > contains one or more column components that specify what information should be displayed for each item of data. The data set can include up to 1,000 items.

• ->no need to write inside <apex:pageblock> or <apex:pageblocksection>
• -> there is no required value
• -> the data can be displayed using custom styles
• -> we need to specify column headers explicitly

 
Apex:pageBlockTable – A list of data displayed as a table within either an < apex:pageBlock > or < apex:pageBlockSection > component, similar to a related list or list view in a standard Salesforce page. Like an < apex:dataTable >, an < apex:pageBlockTable > is defined by iterating over a set of data, displaying information about one item of data per row. The set of data can contain up to 1,000 items.The body of the < apex:pageBlockTable > contains one or more column components that specify what information should be displayed for each item of data, similar to a table. Unlike the < apex:dataTable > component, the default styling for < apex:pageBlockTable > matches standard Salesforce styles. Any additional styles specified with < apex:pageBlockTable > attributes are appended to the standard Salesforce styles.

•  ->pageblocktable should be inside of <apex:pageblock> or <apex:pageblocksection>
• -><apex:pageblocktable> has a required attribute called "value"
• ->it uses the standard salesforce page styles
• ->column headers will be displayed automatically

Apex:repeat – This tag is used as for loop(for list) in apex. You can iterate a list.

• -> there is no proper allignment of data in repeat as compared with datatable

Please check below post for code
1) http://www.thephani.com/difference-between-pageblocktabe-datatable-repeat/
2) http://honeysalesforce.blogspot.in/2013/02/difference-between-pageblocktabledatata.html

Visualforce page:
<apex:page controller="sample" sidebar="false" >
<style type="text/css">
    .outBorder
    {
        border:3px outset black;
    }
    
    .inBorder
    {
        border-top:3px dotted black;
        border-left:3px dotted black;
    }    
</style>
    <apex:pageBlock title="Pageblock Table">
        <apex:pageblockTable value="{!acc}" var="a">
            <apex:column value="{!a.Name}"/>
            <apex:column value="{!a.Name}"/>            
        </apex:pageblockTable>
    </apex:pageBlock>
    
    <apex:pageBlock title="Data Table">
        <apex:dataTable value="{!acc}" var="a" styleClass="outBorder" width="550px">
            <apex:column styleClass="inBorder">
                <apex:facet name="header">Account Name</apex:facet>
                <apex:outputText >{!a.Name}</apex:outputText>
            </apex:column>       
            <apex:column styleClass="inBorder">
                <apex:facet name="header">Account Number</apex:facet>
                <apex:outputText >{!a.AccountNumber}</apex:outputText>
            </apex:column>              
        </apex:dataTable>
    </apex:pageBlock>    
</apex:page>

Apex Controller:

 public with sharing class sample
{

    public List<Account> acc {get;set;}
    public sample()
    {
        acc = [SELECT Name, AccountNumber FROM Account];
    }  
    
}

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