I am looking for some advice on buying a PAT Tester. I am looking a buying a tester for my employer who is construction. But with so much choice I confused on which one is best to meet our need,

I just googled pat testers and came up with this one of many -

http://www.patinfo.co.uk/pat-testers.html

PASS/FAIL PAT Testers

These testers carry out the PAT Test and simply display PASS or FAIL by checking the test results automatically against internally set thresholds. These types of testers can be used by someone who doesn’t have electrical qualifications.

Examples of this type of tester are the BattPAT from First Stop Safety and the Primetest 50 from Seaward.

PAT Testers with PASS/FAIL and display of results

These testers combine the display of the results of PAT Testing as well as showing whether the appliance has passed or failed the test. This type of tester is ideal for the beginner as well as the more experienced user.

The KT71 from Kewtech, the HandyPAT 600 from Martindale, the SwiftPAT from Metrel and the Primetest 100 from Seaward are all examples of this type of tester.

PAT Testers with display of results

On these types of testers, the test result is displayed on an LCD display. The user has to interpret these results to work out whether the appliance has passed or failed a particular test. Someone using this type of tester has to have a good understanding of the tests that they are carrying out and the appropriate limits.

The EasyPAT1600, EasyPAT2100 from Martindale and the Primetest 200 from Seaward are examples of this type of tester.

I have absolutely nothing to do with the company.

As Steve sedgwick said above, if you do not have the relevant electrical experience or know-how, you should discuss requirements with someone who does, be it an electrician, electrical engineer or PAT technician (the competent person who/department that is going to be doing the actual testing would be a good start).
This will help identify what range of tests the tester needs to deal with.
When you've got your specification sorted out, do a G00gle search for "PAT tester comparison chart", and the first (non-sponsored) link should give you a good idea what is available.

I have seen all of them but which one to buy? I am sure they will provide training with them

I would personally recommend the ROBIN smartPAT 5000 as it has many preset functions for both 240v and 110v and a very user-friendly piece of kit. It has a built in memory and can be hooked up to your PC (bar coding, print out, record keeping) but personally I find the software is a bit pricey based on the low volume of PAT testing I carry out and choose to record all my data on a works spread sheet.

I paid around £500 a few years ago for my first ROBIN and when it was stolen I replaced it with a second hand model that cost £200 but remember to check the calibration history before buying a used PAT tester and have it recalibrated (costs around £50.) before using it.

I have also attended a two-day C&G course at the construction skills college and found this to be an excellent course and would highly recommend the C&G course to guarantee both competence and confidence.