It really depends on your team composition and how well the game is going for you. If you're playing semi-support vs heavy AoE, then Mek/Treads/Deso works, with assault as luxury. I haven't seen or tested Pipe, but it could be viable vs very, very heavy AoE. If you farm like a beast, then a rushed radiance works well, maybe get shiva after that for AoE rape. More often than not, deso is the orb of choice; treads/deso/assault makes for a tower destroying monster, especially with the new assault.
If your team lacks disable, then, by all means, get guinsoo.
Skadi is meh, imo. Visage already has a massive slow, and you could get more damage/health for cheaper elsewhere.
Your ulti has a variety of uses, and it is only limited by your ability to micro. You can stack/farm neutrals, use them as wards/scouts (although, that got nerfed quite a bit; it still works ), and they also serve as a big boost of DPS, even early on.