I’m partial to Stihl - but starting level/home owner intended trimmer...quality is near equal. Used both and Echo is probably a tad more reliable..but also less torque.
The “big project” wording makes me lean towards Stihl as a recommendation - just because it sounds like your doing more than trimming a thin line of knee high grass. String trimmers can all do that - but if it’s thick grass and other things - you need a brush cutter with a blade.
Right tool for the right job - it’s like trying to mow a hay field with a riding mower. You “can” do it - it will be slow, you will bog down the best of mower eventually - where the worst example of a proper tool will do it twice as fast and never miss a beat.