I would prefer you buy more bitcoin but if you're satisfied with the number of bitcoin in your portfolio you can go ahead with top Altcoins or infact go for coins that are currently performing fine and take them only on short term investment but id you find a project which you're convinced enough to hold for some kind long period not years specifically but within a good time frame you can add them up.

But perhaps all this advise are only mere suggestions not a professional advise so you're prone to losses hence you should trade with care.