LongListSelector conflict in WP8 SDK and SilverlightToolkit

I trying to compile one of my app in the WP8  visual studio and have the following error.  The  type 'Microsoft.Phone.Controls.LongListSelector'  exists in the silverlight toolkit Microsoft.Phone.Controls.Toolkit.dll'  and in the Microsoft.Phone.dll'  (see error below)

I had installed Silverlight using NuGet.

Which LongListSelector'should I be using in the XAML?   Any advise is greatly appreciated

" The type 'Microsoft.Phone.Controls.LongListSelector' exists in both 'd:\Visual Studio 2012\Projects\XXXXXXXXXXXXX\packages\SilverlightToolkitWP.4.2012.6.25\lib\sl3-wp\Microsoft.Phone.Controls.Toolkit.dll' and 'c:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\WindowsPhone\v8.0\Microsoft.Phone.dll'  D:\Visual Studio 2012\Projects\XXXXXXXX\XXXXX "

Note : I have masked the project name in the above error message.

It appears that Long List Selector is now packaged as part of the SDK 8.0. Unless you come across a need that Microsoft.Phone.dll doesn't cater (I don't think for the moment there will be any for now), use the built in one.

 One more question,

    Which toolkit should be used for apps being ported from WP7.1 apps to WP8. Is it the new Silverlight toolkit or the Windows phone toolkit found in this link  http-://phone.codeplex.-com/releases/view/96743

     Is there any documents  or guidelines for porting WP7.1 apps to WP8 ?

You should use the Windows Phone Toolkit. It's been refactored (with LongListSelector removed, etc.) to work with WP8 SDK.