Here’s a two line review of each place I’ve been to in Thailand.
Koh Samui, Koh Pha Ngan – Crazy party scenes, 36 hour raves etc. You don’t have to party that hard if that’s not your thing, but that’s pretty much what these two islands are known for. We spent 2 days here. One to party, one to recover.
Koh Phi Phi – less noisy, but great fun, very beautiful. Super lazy, nice place.
Koh Lanta – great place for scuba, snorkelling and watersports. I fell off a water scooter here, but that’s only because I tried to start it by leaning it to one side like my Uncle’s Bajaj Chetak.
Similan Islands – haven’t been here but it’s supposed to be bloody amazing. Super private beach scenes.
Krabi – rocky island so looks quite different from the others. Very touristy. Great for massages, junk shopping, drinking on the beach.
Phuket – very beautiful but full of honeymooners. Similar to Krabi but looks different.
Note: High chance of being photobombed by uncles in translucent VIP Frenchies in both Krabi and Phuket.
Pattaya – Sleaze central. Interesting if you’re curious to see the underbelly of Thailand. Tons of Go-go bars, strip joints, shady massage places. The place smells of sweat, cheap perfume and human rights violations. Not much else.
Bangkok – Great city. Absolutely amazing street food, bars and shopping scenes. The shopping scene for women is especially insane at MBK, Platinum and Chatuchak. Two days at least. Lots of touristy things to do too – like temples etc.
Other places to consider – Chiang Mai, Chiang Rai
Hotels / resorts: Tripadvisor is the only site that doesn’t post fake reviews. I usually research on TA, and book on Agoda to get a deal.