What class to Roam within Wvw solo or duo
Tl;DR: Plenty of classes are popular for roaming and very efficient at it, but all differ slightly in playstyle. Only you can decide which class you’d have the most fun with, there’s never a ‘best’ option because every class has it’s counters. I’d pick Thief is you enjoy being in the enemies face whilst bursting them down and you value extremely high escapeability and don’t mind being very glassy. Ranger is your best bet if you enjoy keeping a distance between the enemy and yourself whilst still being able to do considerable damage.
As Thief you’ll most likely be running either a glass-canon D/P spec focussed on bursting down enemies or a P/D spec more focussed around dwindling enemies down with Conditions whilst you’re hard to catch due to Stealth. Both are rather efficient though I personally feel D/P pulls ahead mainly because of it’s utility; Black Powder allows safe-stomps on multiple classes (e.g. Engineer/Warrior) and Headshot can be incredibly valueable in teamfights to interrupt stompp/rezzers, or solo to simply interrupt people’s healing skill or other vital skills.
A Thief will always be rather squishy, relying on smart positioning and stealthing for not only damage but also survivability and will almost always be near the enemy (P/D can kite a bit, but still ‘needs’ CnD.) I’d decide whether you enjoy that or not.
Ranger currently seem to be running the oh-so-popular Power Ranger spec with Longbow or a Trapper Spec with Superior Rune of The Trapper. Just like Thief one build is a glassy Power-Build, how-ever a Ranger focusses most of it’s damage from far away, having Point Blank Shot/Wolf F2 to recreate a gab and Lightning Reflexes/Signet of Stone for survivability. Along with Immobilize (Entangle/Spider F2) for survivability and to make Rapid Fire undodgeable. Great spec if you enjoy fighting from Range more. Greatsword is there in case you get forced into melee and it’s damage nor utility is too shabby.
The Stealth Trapper is a bit of a mixture, you’ll still be kiting foes around as much as you can (mainly with Shortbow and Axe/any for Conditions) whilst dwindling down their health. Putting traps down for foes to walk into and provide escapeability for yourself (thanks to Superspeed from the runes mainly as trap-damage will also reveal you.)
In the end it simply comes down to what you enjoy playing.