ok firstly.. you need to choose between two first..
full touchscreen phone[SE Vivaz] or touchscreen phone + sliding physical qwerty keyboard[N97 mini]
decide this first...then i'm sure you will make your decision quickly..

SE Vivaz VS Nokia N97 mini

I'm just comparing differences.. not similiarities..

1. No Qwerty keyboard DRAW  VS has physical qwerty keyboard DRAW
If me.. I would go for physical qwerty keyboard... its easier to type message/words..

2. No stereo speaker LOSE VS has stereo speakers WIN
of course stereo speakers win

3. 8mp camera with stunning HD video recording,has touch focus DRAW VS 5mp camera[carl zeiss optics] with dual LED flash DRAW
Vivaz win in term of HD video recording.. but the flash isnt as good as N97 mini's ..so.. its draw..

4. no secondary camera LOSE  VS has secondary camera WIN
for me.. its important to have secondary camera[who want to make video call using back camera..?? ]

5. powerful processor with graphic accelerator WIN VS slower processor LOSE
Vivaz has better processor.. and the important thing.. is it has graphic accelerator[really nice in gaming and 3D graphic]

Vivaz really pawn N97 mini at point no.5.. At point no.3 Vivaz should win.. but for me.. the flash is important too especially at darker place..