I attended the Miami Open last year. None of the outer courts at Miami, including Grandstand, have what I'll call wraparound seating, i.e., seats that are in the corners of the court. All the seating areas are metal, though the seats themselves at Grandstand (as well as a few at the Butch Buchholz court, the #3 court) do have molded plastic backs. Also, the upper level south baseline seats at Grandstand are reserved; those are probably the best seats on that court. (When I went in March 2025, I attended for two days and had main stadium reserved seats for both sessions both days, so I needed to sit in the unreserved seats on Grandstand.) Having said that, the north baseline seats at Grandstand worked fine for me; the sun is the only major negative with the unreserved north baseline seats relative to the reserved south baseline seats. I'll note the south baseline seats are near the south end of the grounds, so foot traffic there is less but you're also more removed from the activity of the tournament there.
As for what session to buy, like other tennis tournaments if you want to maximize your bang for your buck, you'll want to buy DAY session tickets so you enter before play starts and potentially see any outer courts matches the entire day. I personally prefer buying main stadium reserved seats at tournaments so I have maximum flexibility about the matches I can watch (reserved seat in the all reserved main stadium, access to the unreserved seats on all other courts).
Some other thoughts about my Miami Open experience:
*Everything was extraordinarily expensive, more than at Indian Wells (which I attended in 2024), which itself was more than at the U.S. Open (which I've attended 8 different years, most recently in 2024).
*You'll need to buy parking in advance. Unlike at Indian Wells or Cincinnati (went there in 2022), there are no free parking options. IIRC, the cost was $40.
*The courts at the southern end of the grounds east of Grandstand (which includes Court 1, the #4 court at the tournament) feel somewhat removed from the main part of the grounds. Relatively few people go over there. I was able to sit in the first row behind the baseline for part of a Jakub Mensik match there last year.
*The grounds are spacious at Miami and IMO they've done a really good job making a facility that was built in the parking lot of a large stadium NOT feel like it was built in the parking lot of a large stadium. The Hard Rock Stadium site was nowhere near as crowded at the USTA NTC (U.S. Open) or Indian Wells Tennis Garden, both of which sell too many grounds passes IMO.
*It is a bit of a hike to get into Hard Rock Stadium itself if you have tickets for the main stadium. You have to go up a lot of ramps.
*The Hard Rock Stadium reserved baseline or corner seats, which are temporary seats set up on the stadium's football playing surface, are actually pretty good seats except for the structure of those seats being made out of aluminum. The biggest negative with the temporary, on field seats inside Hard Rock Stadium is there are limited concession stands in those seating areas; you need to head over to the main stadium concourse to buy most food and drink. You'll also want to keep in mind sun angles if you attend day session or early night sessions matches inside Hard Rock Stadium. In general, the closer your seats are to the main, permanent part of the stadium, the more shade your seats will receive during the day.
*EDIT: I forgot to mention this previously, but there are limited water refill areas at the tournament. The U.S. Open, Indian Wells, and Washington (which I attend for multiple sessions every year; I live 3 miles away) are much better in this regard, while Miami and Cincinnati are lacking.
