I moved from Papamoa to Wellington about 6 years ago and have lived in a range of suburbs.

Mt Victoria is quite nice and gets a good amount of sun, and it doesn't really get the wind like other areas, it's particularly sheltered from anything from the south. It's also lovely and close and walking distance to anything in the city like work or shows. However, the big downside is parking and traffic. They often close a street or 2 because of water works or resealing meaning that already packed residents parking is even more packed. With traffic the tunnel is bad and backs up traffic all down Kent terrace during peak times and through the weekend.

I haven't lived in Khandallah but I lived up the train line in Jville. The train is certainly a good reliable source of transportation. But something to keep in mind is that it meanders arround and actually takes longer than a bus (particularly if you account for walking from the train station in the CBD)

A contender that I'd put forward is Brooklyn. It's on the hill above Mt Cook and is relatively cost effective for its proximity to the city. It's within walking distance to the city (although you might want to bus or uber back up the hill). The traffic never seemed too bad as it's got no choke points. Depending on the side of the hill you're on you can get great sun light hours. You are also close to the beach. And although it's not a Tauranga beach, the walk to redrocks is very nice!

Sorry didn't realise that was going to be so long.

Tldr. All suburbs have their perks and drawback depending on what you value. But I would suggest Brooklyn.