If I were you, I would try Clomid first and see how it works. It is a standard of care. Long term Clomid has been studied well in men, while long term Nolvadex hasn't been studied in men to the same extent.
While some men report less side effects from Nolvadex than from Clomid, others report more. Much of this is anecdotal and in the context of bodybuilding cycle recovery. I have personally never seen anybody report positive sustained results from Nolvadex as long term HRT lasting years, but maybe others know of such reports, in which case I'd be interested in seeing them. As for side effects, for example, it turns out that men with breast cancer (yeah, it happens to men too) have a very hard time adhering to their Nolvadex regimen because it causes many men to lose libido - to the extent that not even cancer can make them take the medication. There are also some serious possible vision-related side effects attributed to Nolvadex - it tends to form possibly permanent crystals in the retina of some patients. It may cause blood clots. Etc.