Absolutely 100% go for the RC18T. I have not owned a Mini LST but I've worked on plenty, and driven even more. They don't track straight, aren't as tough as they should be, etc. My RC18T was absolutely bulletproof, jumped awesome, handled unbelievably well.
The only downside to the rc18t is that in loose dirt, the gears tend to accumulate rocks, but it's nothing 30 seconds and an X-Acto knife can't fix.