I almost never take this option, but I think about it sometimes. I'd always be afraid of forgetting to use it or differentiate the Champion's attacks however, since I tend to roll all of a unit's attacks out at once . For 25 points, that leaves some semi-decent Magic Weapons- ASF, +1 Attack (4 in total!), +1 to Hit (always an underrated one), etc. Some of the others are little-used because they're iffy, but might be fun (Wounds cause Stupidity or Lost Attacks... at only 5 points, why not?). They might be a fun use of the weapons we choose not to stick onto major Combat Lords & stuff like that. Has anyone else tried this?
Give him an extra attack, have the skavenpelt banner in the unit, get wyssans wildform off and you have a cheap WS4, S6, T5, A5 champion lol. He'll not have as good a WS as most enemy heroes, but your cheap champ will be able to eat warrior priests for launch, for more or less the same price. Lol
I made a minor mistake. Giving him the +1A sword will give him the following stats: WS4, S4, T4, A4, AS3+. All that for 44pts. Now add magic and magic banners. A warrior priest comes with light armour, handweapon, hatred for the unit, 3 bound spells and the following stats: WS4, S4, T4, A2, W2, AS6+ without any upgrades and costs 65pts. The champs biggest issue is that he would probably die due to striking last against most targets. So maybe give him the initiative or ASF sword and hope that he'll do two wounds in a challenge. Depending on what your goal is with him.
I think Gold Sigil sword is probably the only one worth considering. Cheap, ups initiative, and you can hit ethereals. This all said, usually I don't upgrade mine