As portages go, the major difference is that the big hill coming from Cedar to Catfish is steeper than hills between the Nip and Catfish or Burntroot (don't know what option you consider). The way you describe your party - it doesn't matter which direction you take. I consider all lakes on your route to be prime destinations (though Catfish tends to be too crowded for my taste) and won't make my decision based only on one portage.

During spring ice-off the Nip could be a tiresome upstream paddle if water levels are high. Travelling up the Pet from Cedar, however, is not normally a problem as the fast-water approaches at the downstream end of the ports are short and usually do-able. At lower water levels the trip up the Nip from Cedar to Nadine port and further up to the connection through to Burntroot (via Remona and Whiskey Jack) is fine and people do it often enough.

Personally, I would go over Unicorn Hill.  Once reaching Catfish, I would camp on Lynx Lake.  Nice site on point on your right as you reach Lake and good trout fishing to boot.

I have done this same trip a few times in the past.  I would definitely camp on Whiskeyjack rather than Robinson as campsites are better, water is clearer than Robinson, and again some excellent fishing for trout again.  When you reach Burntroot after the short portage from Perley, there is a root cellar that is worth seeing.

Have a good trip and as I said previously, if you are planning on fishing you’re in prime trout territory.

Thanks for the responses all! It's much appreciated to someone who has yet to access out of Cedar Lake.

Martin - excellent point about the Nip water levels. I plan to do the full Nip (from Big Bob to Cedar) next 2021 Spring with a fishing buddy.  I was not a fan of the Tim during low water levels in 2019 so I will try to stick to 'Gonq rivers in the Springtime. Thanks.

Evan - love yours videos! I believe I saw you do this prospective loop in one of your videos? Thanks!
What's your go to single-malt? My personal favourite is a Lagavulin. 

Bo - You''re quite the Algonquin royalty sir! Thanks for the trout fishing pointers - we will hopefully put them to good use! Great point about using Lynx Lake instead of Catfish to stay away from the 'crowds'. We may be a bit louder group as we're 4-6 people and we don't want to inhibit others' Algonquin experience. 

Eddy - great point about not gunning for a specific campsite. We've all been skunked a few times on certain lakes and it does smart if you've been anticipating it for months! 
 

Based on the your projected route, Catfish to Burntroot, I highly recommend you begin at Petawawa and suggest you skip Lynx all together.  Why would you want to make that unnecessary and time consuming detour? To "avoid crowds"? There are tons of campsites on Catfish, unless you're heading in on a long weekend. Then yes, it may be tough to find a decent site. Incidentally, the fishing is not that great in Lynx anymore. Keep on trucking, I say. When you reach Catfish, try and scoop the campsite east of Shangri La if you can.  It's a beautiful semi-secluded site.  Also, the port between Ramona and Nipissing River is easy walking, but it certainly is long. I single carried that non stop at 50 years old. Yes, you read that right.

And finally, you're going to be traveling through some prime fishing areas. Shoot me a PM and I'll give you a fishing suggestion worth while, if you're bringing your fishing equipment.