Hard to pick just five!!  I reserve the right to change my mind in the next 20 minutes, but here is my list as of now:

Tony Murcheson - if this were a top ten list, she would be the top five choices.  But since this is a top five list, Tony will simply hold the top spot.  She is the NEXT MEN book for me.

Shaman - I dig everything about Shaman - his powers, his role as a memeber of Alpha Flight, and his role as a father. 

Theela - I went into FRONTIER DOCTOR for McCoy, but I return to the series often for the wonderful team of McCoy, Theela, and Duncan.  They are a great team, but Theela is a standout among JB characters.

Donna Wojciechowski - WHIPPING BOY  is one of JB's best.  Bonus points for Donna and Walker Stone also appearing in NEXT MEN

Michael Swann - COLD WAR is a fantastic book, and a big part of it is Swann's cool in a Cold world.

Sasquatch - Maybe the most visually interesting character John created. Nearly Hulk-level strength, amazing agility and one of the greatest scientific minds in the MU. I only wish John would have made him a hockey player rather than a football player...

Box - A cripple who created a powerful suit of armour in his apartment? Yes sir. Wait, he also designed a phase technology for the wearer to get into the armour. That is a whole 'nother level of sophistication!

Toni Murcheson - Tough, capable, resolute and she cares. 

Kitty Pryde - For many years (probably until shortly after she joined Excalibur) she was my second fave character. Then I noticed that the Kitty I was reading wasn't the same Kitty I fell in love with. 

Subtlety and/or letting readers use their imaginations isn't the 'new' style lol.

I thought a paraplegic hero cybernetically controlling a suit of armor was brilliant.