Unfortunately, haven't played Border Wars, but I've played En Garde several times and I love it!
Compared to other small skirmish systems (Donnybrook, Mordheim) it's by far my preferred one. The system of combat pools and predicting how offensive/defensive your opponent will be in any given combat is super fun and can lead to amazing moments. I've had plenty of those - plucky soldier inexplicably taking on experienced fencers, winning 3-on-1, etc. They don't happen often, so it doesn't feel cheap or unrealistic when they do. But I had situations in my club when people would pause their games for a second to watch a particularly important fight, just because it is fundamentally a fun think to do - you and your opponent staring at each other while choosing how many attack and defense counters to choose underneath the table, the big reveal and "oooohs" and "aaaahs". If you are keen on a little bit of theatrical improvisation, you can make the game an absolute joy for everyone around.
I really like En Garde, and would recommend it. The rulebook is relatively cheap and copies constantly show up on eBay (at least in UK). I think that even if you decide for Border Wars (which could be a great game in and of itself, I just don't know), buying En Garde may not be out of the question 😁