While both of these procedures do a great job on fat, they don't help stretch marks at all. That is something that can be helped by a tummy tuck, but the trade off is that you will have much longer of a recovery period with a tummy tuck than liposuction. Tummy tucks take about 12 weeks to recover from and have a huge scar on the bottom of the belly that can often be unsightly.
In fact, if you have tumescent liposuction done in combination with either of these, your recovery can be as little as one day. That means you can be back at work by the next day and all you have to do is wear a 'spanx' like garment for one month. That is why this makes so much sense versus a tummy tuck, although it doesn't affect stretch marks at all so if that is your main goal, then a tummy tuck makes more sense.
One last thing that needs to be evaluated when choosing tummy tuck vs liposuction is that your belly button won't be the same if you do the tummy tuck. It looks odd and in a swimsuit is very obvious usually. Just a thought and good luck whatever you do.