I just got back from a one-night stay in BKK, will be back in a few weeks. I stayed at the Pinnacle for several nights, last June/July/August, and also in April this year.
Compared to past years, I have found the Pinnacle getting busier and also working its staff harder--the turnover is much higher than it used to be. The bedsheets are often NOT changed between guests--look for long hair when you get into the bed. I've found it 2x.
However, the location (especially now that the Subway has opened), reasonable price, and the ok breakfast has kept me going there for many years, especially once the Tarntawan got to be so expensive! Now, this brings a "deluxe room" at the Pinnacle up to almost 1800 baht--only 700 less than the Tarntawan, which is markedly better, IMHO.
Anyway, last week I stayed at the Tarntawan, and was impressed--probably 75% of the staff is the same as 3-5 years ago. Room service is still nice, 24-hour breakfast is wonderful (!) for those who get up late and/or have early flights, and, most surprisingly, they have FINALLY started to upgrade the rooms: mine had new furniture, flat-screen tv, etc. Still not really worth the 2500 baht, but at least I don't feel crazy for booking there!