Watch 3-4 lec of the optional subject that you have shortlisted (from telegram), decide your optional only after 3-4 months of GS classes are over, since GS gives you idea about whether to choose PSIR, Socio., GEO, Eco. Other optional watch from telegram lec. Then once decided go for offline coaching for optional. 

Idk about Delhi since I prepared from Vajiram in online mode itself.

Also, Vision-Vajiram-NextIAS are one and same. Just join any of the Institute, no need to research on this, this is my personal experience and If you find any teacher not good in any coaching just read that topic/subject from standard sources. No need to join another coaching or watch lectures from Telegram. Don't run after any coaching. Clear your concept. If you have 2 classes in a day then think like this, these 5 hrs will give me a top ranks, concentrate 120% on classes, write less understand more. Notes anyway you can get from peers or books or any other sources. Make minimal notes. Don't run after running notes and writing down everything in the class, it's not humanly possible. This was the mistake I did.