Don't get any of them. They will all be relatively uncomfortable for you.
If you'd like one that will be comfortable for both you and last another few months (or another few years) it would be worth having a look at the babywearing sticky
viewtopic.php?f=36&t=98827 for ideas and advice. Your baby is still young in babywearing terms - with a decent carrier you can carry them in comfort until they are 2 or 3.
Personally I would recommend a Connecta if you want a carrier with buckles
http://www.connectababycarrier.com/
a Storchenwiege Leo if you want a woven wrap (a stretchy would pretty much be a waste of money now your baby is 6 months)
http://www.bigmamaslings.co.uk/zen-cart ... p-129.html
I don't do ring slings, I just use a short wrap so I can't help with those or pouches.
I don't currently have a standard mei tai though lots of people here love Maria's mei tais
http://www.simplymeitai.co.uk/ I have a bamberoo on the way but I haven't got it yet to review for you.
My number one recommendation for a carrier would be a wrap conversion, particularly those by Ocah
http://www.ocah.typepad.com/ I have 2 and they are amazing. Unfortunately she has a waiting list so you probably don't want to wait for one.
Have a look for babywearing forums for a forum full of advice and a for sale board where you may pick up a bargain.
I know it's confusing with so much out there but unfortunately it is personal choice - many people will tell you how great ring slings are but personally I don't like them much. I really recommend a 2 shouldered carrier for your comfort. have a think about what sort of carrier would suit you best - are you wanting a 1 shouldered carrier you can pop them quickly in and out of? Would you prefer a 2 shouldered carrier so that you can carry for longer each day? If so, are you happy to try a wrap? Or would you prefer buckles? If you answer these questions we can help you more
I would recommend
http://www.mamanatura.co.uk/ and
http://www.bigmamaslings.co.uk as vendors. Any sling on these pages will be a well designed carrier.