The best strategy for small investors would be to purchase bitcoin monthly for a fixed amount of fiat (say 100 USD) and hold it. It'll come in handy when USD goes bust (come april 2018)
Most coins are now BTC imitators with some slight variation. ETH is tiring complete and is aimed at smart contracts, however the supply of ETH is relatively unlimited, unlike BTC which has a fixed amount.
Alt coins vary things like total number of coins or block rate and others look to improve aspects of BTC such as anonymity (Zcash and Monero) it's worth looking at the tech behind them to see whether you think it is worth investing in.
Many early coins such as PPC and NVC are essentially scams but something like NMC was trying to do something genuinely new, although the last I heard a serious security flaw existed in NMC which if it was widely understood should mean the death of the coin because it is no longer being developed as it is mainly a speculative vehicle it has stayed alive.
XRP I think is another one to keep an eye on. It's the only other one I hold besides BTC/ETH. It's the 3rd largest behind the two and is targeted to FinTech, which is a nice industry to be involved in (if successful). The risk is whether or not they can overcome barriers to entry (which is pretty high in finance).