pennybridge

I know we are probably very few. If someone like it as much as i do, or is eager to try i could highly recommend Lola's Kitchen. Located closed to sukhumvit soi 49.

In the picture. Lumpiang shanghai, lechon paksiw, pork sisig & lechon kawali. Masarap!

I've stayed at Citrus Suites Soi 6 the last few times in BKK. Aside from a mediocre breakfast buffet, it has a lot going for it. Location is hard to beat.

Seems like a lot of folks who have stayed there say there is nothing wrong with it, that it is a low-end property but a clean one. That said, if the idea is to stay in a hotel within shouting distance of Nana Plaza, there are several nicer options on Soi 4 in the same price range like Lohas or Citrus Suites. 
 
 

Yes, exactly what Mikel said. The pool isn't the typical rooftop setup. Plenty of seating with lots of nooks and crannies for sitting with LBs. The rooftop restaurant also serves up a killer hamburger that rivals what Firehouse in Bangkok offers. Overall, it's a solid property and as said before it's about a 3 minute walk from CIB.
A couple of downsides: The lobby restaurant tends to get overwhelmed at breakfast. Tables don't always get cleared promptly enough and it causes customers to stand in line for 15 minutes or so waiting minutes to be seated. It's not a fun way to start the day when you have a pounding hangover from the night before and just want something to eat. 
I stayed there twice over a 10 month span. Both times the elevator music was nothing but Eric Clapton's "I Shot the Sheriff". As a bonus, they always had the volume turned up way too loud.  I have always hated that song. Hearing it in G10 elevators about eleventy billion times over 2 years was worse than waiting in line for breakfast every day. Way worse. 

S15 looks great, might give it a try as well. I do prefer a hotel with a pool. S15 looks promising though with great location. I got a good deal on Agoda at Galleria 10. Deluxe Chill Room, 820 baht/night (maybe its the normal rate?). Only staying 2 nights there though before i go to Pattaya.

S15 looks great, might give it a try as well. I do prefer a hotel with a pool. S15 looks promising though with great location. I got a good deal on Agoda at Galleria 10. Deluxe Chill Room, 820 baht/night (maybe its the normal rate?). Only staying 2 nights there though before i go to Pattaya.

Last time I was in Chiang Rai 3 of us went to the White Temple, Blue Temple and Baan Dam Museum in about 6-7 hours time including a quick lunch. I was driving a rental car and was staying in a village outside of CR. 
You might search for a tour company that has drivers that will pick you up at the airport and drop you off when finished that you can book ahead of time. They might also give you a good idea of how much time this would take.
The North is certainly beautiful but this time of year the air pollution can be horrible. After Songkran is best but who knows. In May the rains come and clean the air. This year the air pollution has been minimal but I don't expect it to last. Today the readings are in the Red Zone. That is 150 to 200 aqi. See the chart.
https://aqicn.org/scale/

Fly out of DM early and hire a car at CR. Easy and cheap. The roads are excellent and White Temple is well sign posted. Singha Park is ok for lunch and the Opium museum is a trek but not hard to find. You'll come back via the junction of Laos, Burma and Thailand. Plenty of good quality, cheap guesthouses and streetfood. Night markrt is ok. Up a side street, short distance from the Clocktower are two bars that have Lbs on staff. 
Midday flight gets you homw in time for fun in lower Suk 

If it's your first trip, you probably want to keep the itinerary simple. Maybe 75% Bangkok and 25% Pattaya. Or the opposite. Up to you. There is loads to see and do just in Bangkok for a first-timer. 
I think most guys here go directly to Bangkok from BKK airport and make their jaunts elsewhere later in  the trip. On most trips I spend a month.  It's usually 2 weeks in Bangkok, then 1 week in Pattaya, then back to BKK for another week. Sometimes I go with my girlfriend to visit her family in Lampang for a few days. Other times we go to Hua Hin or Chiang Mai instead, but I always stay "headquartered" in Bangkok. 
No need to mess with U-Tapao because BKK or DMK airports are only about 2 hours from Pattaya and you can fly anywhere from there with many more schedule options. 
I don't care for Phuket and the LB scene is fairly minimal there anyway. I have never been to Samui, maybe others can help you. 

6k baht will get you a room in most of the upper end hotels. Landmark meets that criteria. It's elegant and lot of guys like it because of its proximity to Nana. Adelphi is good, but it's a bit overpriced when compared to Phachara which is closer to Nana and offers you almost identical rooms for less. I don't know anything about Doubletree. I have stayed at Galleria 10 in the past, and it's perfectly acceptable. Forget that "walk of shame" stuff. I promise you that the staff at any of the hotels around lower Sukhumvit don't care what you do because they have seen it all eleventy billion times in the past. They don't care. REPEAT: They don't care. As for other farang guests whose delicate sensibilities are shaken by the sight of the world's oldest profession, why in the hell did they choose a hotel in the world's largest red light district?  Their issues are their problem, not yours. 
If you want to stay in suite type rooms, I also like In Residence suites on Soi 13 (adjacent to Radisson suites). They have large suites and a good pool on the roof. Soi 13 is next to Soi 11 but without the traffic and noise found on 11, meaning you can enjoy 11 easily without having to actually stay there.