I'd personally say Southampton is better for Engineering compared to Leeds. Leeds is a great uni and I've applied there but Southampton is a notch better. Pretty sure it wouldn't make too big of a difference if you went to either especially as in engineering it doesn't make a massive difference but if you care about which is better then go for Southampton. It's also worth bearing in mind that you'll probably be more likely to find a job in the south of England compared to the north if you want to work for a "big/international" company. Good luck!