Thailand forum

I spent about 4-5 days on Koh Kradan a year ago (on my own) - along with Koh Ngai and Koh Muk. Out of the 3, Koh Kradan was my favourite by far. I think it would definitely appeal to someone who is happy being on their own - it's a very quiet island, a nice beach and good snorkelling, etc.

There have been some discussions previously on TF:
http://www.travelfish.org/board/post/thailand/7393_ko-kradan-paradise-lost---how-to-contact-wally--
http://www.travelfish.org/board/post/thailand/8759_here-is-more-info-on-paradise-lost-ko-kradan
http://www.travelfish.org/board/post/thailand/9365_accommodation-on-ko-kradan

.. and some info on accom here:
http://www.travelfish.org/accommodation/thailand/southern_thailand/trang/ko_kradan/all

FWIW - I stayed at Wally's (Paradise Lost) and thought it was perfect. It has a pleasant open air restaurant/hang out area and is probably the most popular place to eat on the island (but still definitely not crowded). You will find opportunity to join others during dinner if you want, or eat a bit earlier/later to avoid the crowds. Cost for me in Feb was 600baht/night for a fan bungalow with shared bathroom. Food is a bit more expensive on these islands than you would pay elsewhere, but not exorbitantly so. I could have happily spent another few days there, but I also wanted to move on to the other two before returning home.

Get a 2nd class berth on the overnight sleeper train from Bangkok to Trang. You can chose between upper and lower bunks (lower bunks have more room) and a fan or A/C compartment.
Traveling overnight saves you the cost of a night's accommodation so it's an economical and time efficient way to do it. There are VIP buses too but personally I prefer the trains because you can stretch out properly.

More details here (timetables, pictures of the trains etc)

www.seat61.com

When you come out of the train station in Trang you'll see travel agents who can arrange transport to the pier and Ko Kraden. There's one on your left called Sea Breeze just as you leave the station which I haven't used for a few years but they always used to be very helpful.

Comparing Koh Kradan and Koh Phi Phi like comparing... apples and oranges, black and white, heaven and hell. Phi phi would be my worst nightmare; Kradan was bliss. But it depends on what you looking for. Kradan is very chilled out, quiet, still and peaceful - aside from the odd boat full of Thai tourists that land for an hour, doing loud karaoke while having their lunch. But they're gone again in an hour, and you can walk around the corner to avoid them anyhow.

Phi Phi is...well, the opposite - although I believe it's a bit more laid back in some of the remoter areas of Phi Phi. But I think it's also much more expensive in those remote places.

Can't comment about Koh Lipe as I haven't been there - but suspect it's somewhere between the two in terms of 'vibe', etc.

If you are planning on staying in Railey or thereabouts, (or possibly Phuket and even Koh Lipe?), they do run day trip snorkelling trips which are pretty good. They often stop on Phi Phi for lunch, so you can get a taster that way.