Hi, thought I would share my experience as about three years ago I was pondering the same question. This is my history of Amiga buying and hopefully you will learn from my purchases.
I first bought an Amiga 500 - yes it was cheap but the disk drive was very unreliable - some games loaded one day and then failed the next.I think I spent £20 but feel this was a waste of money and I didn't keep the computer that long. I also forgot how much space the amiga 500 takes up, especially if you are using the TV module.
I then got a CD32 - it came with the 444 game disk cd and meant that it had most games I wanted. However it didn't have a disk drive to save games like Monkey Island. I could have bought a SFX-1 (think thats right) which turns the cd32 into a A1200 but these cost about £100+ on ebay. I ve still kept this as even though it was a machine with a short life there are some great games available for it.
I then bought an Amiga 600. Loved the smallness of the machine - it played most games from floppies. I used easyadf from amigakit to transfer games to disk and I bought a hard drive to save Monkey Island. Everything was fine until I started to get interested in WHDload. Most games wouldn't load due to limited memory on the Amiga 600. If Commodore had made it easier to expand the Amiga 600 it could have been a brilliant addition to the amiga family of computers.
I then ended up buying an Amiga 1200 with a CF hard drive with WHdload - in order to get larger games to play I also ended up buying a blizzard and extra memory. Since then it has been my most used retro machine and I wished I had bought it from the start as I would have saved £100 to £150 which is the costs of the A1200.
My advice would therefore be - if you have basic computer knowledge go for the Amiga 600 and use Easyadf - you can run most games on the Amiga 600 and use re-lo-kick for earlier games and it won't take up much space. If I hadn't got interested in WHDload I would have still been happy with this computer - it is easy to find replacement parts especially disk drives as it uses the same type as the A1200.
If you are confident with computers get the Amiga 1200 - as soon as you use Whdload you will never look back - the quickness of running SWOS from the hard drive makes it difficult to go back to the original disk load method.
Which ever computer you go for don't forget the wonderful amiga pd games which were released. www.amigapd.com