I did this trip just the other day on Thursday. Got a £3.65 Get Around day ticket with my Key - great value! Unfortunately I didn't get a Citaro on routes 58 (despite a couple of attempts, sigh) and 2A/2C.
© denotes a Citaro. dep. indicates timetabled departure; any notable delay to that service is shown as [x late].

Anyway, this is what I had on the day:
5233 X85 Hexham - Newcastle Eldon Square dep. 0843
5293 43 Newcastle Eldon Square - Metrocentre dep. 0935 ©
5275 49B Metrocentre - Winlaton dep. 0958 ©
5275 49A Winlaton - Metrocentre dep. 10xx ©
5347 X66 Metrocentre - Gateshead Int. dep. 1052 ©
4918 58 Gateshead Int. - Heworth dep. 1114
5359 4 Heworth - Washington Gall. dep. 1146 [8 late] ©
4920 2C Washington Gall. - Sunderland dep. 1241
5303 35A Sunderland - South Shields dep. 1327 [4 late] ©
5328 27 South Shields - Heworth dep. 1413 ©
3978(?) 58 Heworth - Gateshead dep. 1520 [1 late]
3965 21 Gateshead - Newcastle New Bridge St. dep. 1553 (actual)
5338 309 Newcastle Haymarket - Battle Hill Dr. dep. 1613 ©
*(Arriva North East)* 7622 308 West St. Wallsend - Newcastle Haymarket dep. 1644 (actual)
*(Arriva North East)* 4664 685 Newcastle Eldon Square - Haltwhistle dep. 1745 [18 late]

All in all, a good day out. The 1510 Heworth to Hadrian Park 58 didn't show up at all so everyone went onto the 1520, which was an 02-reg Vyking (absolute shed) which only went as far as Newcastle. I bailed at Gateshead Interchange and hoped to get the next bus up to Eldon Square. I got on a 21 (not a B5LH hybrid unfortunately) and immediately I was hit with the smell of poo; there was a drunk man asleep and I guessed it was him (barf) so I bailed again at New Bridge Street and walked up to Haymarket.
I then got the 1613 309 up to Battle Hill Drive - the light was fading and it was cold; to add to the problem I didn't know where the hell I was and I had to be at Eldon Square for the last 685 of the day back home.
I got off at Battle Hill Drive (Wallsend) and then an artic 58 passed me going to Heworth - annoyed was not the word! Because of the delays/cancellations on the 58 earlier I decided not to wait for the next one and I got an Arriva VDL DB300 back to Haymarket where I pondered what to do for the next 45 minutes or so. It was rush hour and I was half-tempted to have a small trip on the Metro but I (probably for the best) didn't.
I noticed that, at Eldon Square, 5 minutes before my 685 home, there was an announcement saying the 1745 685 to Carlisle will be 5 minutes late. I never knew they announced things like these on the buses?!
5 minutes late was too good to be true, and, in true Arriva style, 4664 was at the stand at 1803 - 18 minutes late.

Absolutely great day, I really did enjoy it. Its a shame I didn't get a Citaro on all routes but I didn't want to risk waiting for the next service where the previous bus wasn't a Merc because it would no doubt mess my plan up.
What really did annoy me was the amount of buses on the 58 route that weren't bendy Citaros - yeah there were a few, but a lot of the buses were the Vykings and generic single-deck Volvos.

I've got plans for another similar day out; next time chasing Wright Solars. However I'll ask for info on those later on.

Sean
P.S if you've got this far, thanks for reading!